ACH: The Route 91 Harvest Shooting

The following is an application of the Analysis of Competing Hypotheses (ACH) to the Route 91 Harvest shooter case, the mass murder of 58 persons attending an open-air music festival in Las Vegas, Nevada, on 1 October 2017. The case came to a dissatisfying close in early 2019 with investigators announcing a motive was not uncovered and likely never would be.

An attempt was made here to ascertain the motive by applying ACH to publicly-available information. ACH does not determine the “correct” answer, but it can identify weaknesses in hypotheses, thus eliminate those that contain too many inconsistencies to support the evidence. It does not rely on opinion, but instead on the considered judgment of the analyst.

For analysts who wish to test their own theories, but who haven’t used ACH in their work, or who are unfamiliar with the process, you’ll find a detailed explanation following the matrix.

A Note About Motive And Mental Illness

Mental illness was not addressed here, per se, in assessing motive. It challenges credulity that it did not factor into the crime at some level; although, a detailed FBI study of active shooters concluded a blanket explanation of “mental illness” as an overarching motive was “misleading and unhelpful.” Paddock used prescription anti-anxiety medication prescribed by his primary care physician, but he did not appear to have a formal diagnosis of mental illness made by a mental health professional. It is acknowledged he could have had an undiagnosed condition.

While the FBI could only corroborate 25 percent of active shooters included in their study (A Study of Pre-Attack Behaviors of Active Shooters in the United States Between 2000 and 2013) had a diagnosed mental illness, the Bureau did find such criminals had a marked lack of resiliency in dealing with stressors. Further, perpetrators faced an average of 3.6 stressors in the year leading up to their crimes. Paddock had approximately seven: 1. mental health (anxiety/depression); 2. financial strain (identifiable downturn in finances); 3. job-related (shutting down of rental real estate partnership with family members); 4. relationship issues (relationship with girlfriend in decline); 5. caregiving responsibilities (aging mother); 6. physical injury (complained of multiple real or imagined health issues, and reportedly had “lingering” injury from slip and fall accident several years prior); 7. sexual stress/frustration (unable to perform).

ACH In Practice: Seeking to Uncover The Motive Of The Route 91 Harvest Festival Shooter

Theories considered during initial brainstorming sessions:

  1. Infamy (living in father’s shadow)
  2. The development/delivery of a complex plan (cerebral exercise)
  3. Family resentment (leave them to pick up pieces without having him to lean on)
  4. Rage due to mental/physical decline
  5. Despair over financial loss
  6. Regain control of life spiraling out of control
  7. Craving to feel something again/excitement (fill emptiness)
  8. Injustice of lost father/vengeance
  9. Distractors that kept negative feelings at bay stopped working
  10. Guns as new hobby turned dark as he unraveled
  11. Despair over life choices, no time to start over
  12. Fleeting renewal of vigor (revive peak mental/physical state)
  13. Mass murder/suicide (lack of empathy/control end of life)

Initial research into the case led to three hypotheses being among the strongest:

  1. Infamy: This hypothesis was based on the FBI Behavioral Analysis Unit Las Vegas Review Panel judgment that Paddock may have been influenced by his father, Benjamin Hoskins Paddock, Jr., a criminal who “achieved significant criminal notoriety.” This theory suggests Paddock sought to leave behind a legacy.
  2. Pent-up rage-lashed out externally at strangers: This hypothesis suggests Paddock’s action was based on taking out pent-up rage on strangers. Paddock had recently experienced a decline in mental and physical health. This theory finds the anger he felt over the decline grew to the point of unbearable rage that led him to lash out externally against strangers.
  3. Internally-focused need to regain feeling of vigor: This hypothesis stems from Paddock’s history of self-reliance and self-sustainment. Declining health–real or imagined–threatened his independence because health was the one aspect of his life he couldn’t control. This theory suggests the amassment and use of multiple powerful weapons satisfied Paddock’s overwhelming internal need to regain peak physical and mental power, strength, and control.


  1. In terms of facts and evidence, what interviewees said was true to the best of their knowledge.
  2. Publicly-available information and interviews, and Paddock’s Internet search history, are a representative and meaningful sample of the larger body of evidence that is available exclusively to law enforcement.
  3. Guns offer the bearer a sense of power; more powerful guns, and/or a higher volume of guns, give the bearer an exponentially grander sense of power.

Findings (based on ACH matrix, below):

  1. Hypothesis #1: Infamy | Eliminated | Paddock displayed a marked lack of interest throughout his life in being placed in the public eye. He was not known to promote himself and did not associate with persons who sought attention. He had no online presence. He refused promotion and recognition for jackpot wins. He took little interest in his appearance, and purchased relatively modest homes and cars. There were no verified accounts that indicated his “famous” father caused him pride or disgust, or that he sought to emulate his father’s lifestyle. He left no notes, manifestos, Web site comments, private conversations, or other clues to explain, justify, glorify, or otherwise promote his crime.
  2. Hypothesis #2 : Pent-up rage | Eliminated | By all accounts, Paddock appeared to have/display few emotions. Multiple persons who knew him well described him alternatively as “mild mannered,” “never violent,” “did not have anger issues,” “did not display behaviors of violence or revenge,” “did not speak in an emotional manner,” was “never rude or disrespectful.” These descriptions did not change over time. He met responsibilities for those within his personal and business circles (girlfriend, mother, younger brother, tenants). He was twice-married and reportedly maintained good relationships with both ex-wives, even going into business with one. He was routinely described as “eccentric,” “aloof,” “a loner,” and “reclusive,” but there were no verified accounts upon his death of those who had known him who reported they “saw it coming” or recalled accounts of prescient behaviors. He apparently accepted the verdict for a lawsuit he filed against The Cosmopolitan for a slip and fall accident that resulted in a “lingering injury.” He was not criminally known to law enforcement.
  3. Hypothesis #3: Regain feeling of vigor | Not Eliminated | Of the three theories, the hypothesis with the fewest inconsistencies was Paddock’s need to relieve real or perceived physical and mental frailty; health as the one element of his life he couldn’t control; and the shooting as an act of fleetingly regained vigor. His background of losing his father to jail and subsequent abandonment, and being raised by a single mother with four sons, led Paddock to be self-reliant and self-sustained. According to family members, Paddock was motivated by “what benefited him personally.” Paddock began collecting guns at age 29. Between 1982 and 2015, he purchased handguns almost exclusively. In 2016, he switched mostly to semi-automatic rifles. The switch coincided with several changes in his life: worsening complaints about health issues including anxiety and depression, fatigue, a “chemical imbalance,” headaches, allergies, and a “lingering injury” from a slip and fall accident; a relationship in decline; the setting aside of a 20-year real estate partnership with his mother and brother; a loss of interest in cruising/traveling, a pastime he had enjoyed for the previous six years; and an apparent downturn in his luck at video poker, a primary focus since the early 1980s (his bank accounts had reportedly dropped fairly significantly in recent years).
InfamyRage (external focus) – lash out at strangersInternally-focused need to regain feeling of vigor
No social media presence even though computer savvyI (would self-promote)NN
Didn’t leave suicide note/manifestoI (would want to promote self/control image after death)C (no respect for others; no need to explain)C (self-focused; wouldn’t feel an obligation to explain actions to others
Bragged to neighbor (Mrs. Judy) about $20,000 poker winC (concept of showing off, bragging)N C (could also be “N”; evidence of pride in gaming prowess)
Wouldn’t shake hands; often wore glovesNC (if for perceived health reasons, “N”; “C” if intended to create distance between self and others)C (assuming to prevent illness because illness= weakness)
Physician thought Paddock may be fearful of medications (took anxiety meds; no anti-depressives)NNC
Relationship with Danley in declineNC (declining relationship as stressor)C (personal life unstable)
No sex; complained of physical exhaustionNC (declining health as source of anger)C (vulnerability of failing health)
Often complained about being sick; doctors told him he had a “chemical imbalance” and they “couldn’t cure him”NC (declining health as source of anger)C (vulnerability of failing health)
Ex-wife said childhood instilled need to be “self-reliant” and “self-sustaining”NN (could hone anger due to future of potential reliance on others)C (facing poor health and reliance on others)
Ex-wife said “not interested in drawing attention to himself”I+NC (history of self-compartmentalization)
Eric said Paddock had “limited interaction” with Benjamin after Benjamin’s release from prisonN (need more info about relationship between father and son in terms of whether his actions stemmed from father’s history) N (need more info about when this “limited interaction” contributed to rage or if Paddock didn’t care) N
Not uncommon for Paddock to be out of contact with Eric for “long period of time”; they spoke “when something needed to be discussed”NNC (confirms relative isolation to other family members)
Atheist: found religious people to be “ridiculous”NNC (stood alone; no religion as potentially stabilizing external/internal force)
Eric described Paddock as a “narcissist”C (need for validation)N (narcissist would not care about the deaths of others but not pertinent to concept of rage ) C (could see how narcissist/self-focused individual could feel special need to retain vigor)
Eric thought Paddock would have sought to be known for “largest casualty count”; wanted to be best and known to everyoneCN (does not necessarily correlate with lashing out in anger) C (in terms of the higher the potential death count the greater the feeling of regained physical and mental vitality)
Eric said Paddock “only cared for people would could benefit him in some way”NN (although it speaks to how he sees/relates to others as disposable)N (although is compatible with his self-focus
Eric said Paddock needed to be seen as importantCNC (assuming “importance” part of need for physical and mental autonomy)
Despite lack of affection Danley said Paddock showed “concern and compassion”I (seeking infamy via the deaths of others contradicts his apparent “concern and compassion”)I (a concerned and compassionate person would be empathetic to others and would not seek to hurt them)N
Paddock sent Danley away mid-September; sent $150K to buy home in PhilippinesNNC (controlling persons around him; confirming status as “solo traveler”)
Bruce Paddock had not seen Paddock since the early 1990s and not spoken to him for over 10 yearsNN (expresses potentially controlling personality, but not evidence of rage) C (shows pattern of isolating self)
Patrick Paddock had no contact with Paddock in 20 years; had no interest in him or any family membersNN N
Patrick said Paddock was “motivated by what benefited him personally”CCC
Nephew said if Paddock hit a large jackpot he would “decline any photographs or recognition”I+NN
Cousin said Paddock’s mother was “angry and bitter” Paddock’s father abandoned her and the boysNN N (although does speak to upbringing and need to be independent)
Cousin said Paddock was becoming “more irritable” NC (on the spectrum of being increasingly prone to anger)C (assuming irritability derived in part from feelings about failing health)
Cousin said Paddock would not see dentist for missing and rotted teeth due to “allergies”NNC (speaks to overall ill health)
Physician last saw Paddock October 2016; only “major ailment” was muscle tear from casino fall in (2011)NNC (disconnect between what Paddock perceived in his health and what his doctor saw)
Physician thought Paddock was bi-polarNC (could explain rage)C (referencing mental and physical health concerns)
1982-2017: Total of 67 firearm purchases; 18 handguns, 1 semi-automatic rifle; majority semi-automatic rifles post 2016, but some shotguns, handguns N (the total number of weapons involved might factor into infamy, but this is referring to dates/patterns of purchase)N (debatable, but don’t see how pattern of weapons purchases correlated to lashing out in anger) C (assume guns gave him sense of strength and security; assume he sought more as his physical and mental health declined)
23 semi-automatic rifles; 1 handgun found at crime scene; 14 firedC (the number of weapons and fire power involved would contribute to infamy)C (14 weapons fired in approx 10 minutes; every time he picked up a new weapon, there was a break in which he could have “cooled off,” but never did; uncontrolled rage)C (multiple weapons; more power)
Mom, Eric, Paddock in real estate partnership for 20 years; dissolved 2016NNC (goes toward giving up elements of life recently; isolating)
Paddock would “purchase the very best rifle but wouldn’t shoot it because he wouldn’t want to get it dirty, to have to clean it” … but also to keep it “pristine, so it would fire properly” NNN
Paddock born in 1953; dad went to penitentiary ’53-56; arrested in ’60, went to prison; escaped ’68, never returned homeNN (would be consistent if anger at father factored into rage, but no evidence he was angry at his father)N (assume his father would not have factored into his decision because no one mattered to Paddock but Paddock)
Father on FBI’s 10 Most Wanted ’69-’77C (this goes toward the FBI theory father’s own infamy factored into Paddock’s actions)NN (Paddock appeared not to factor external persons into his internal processes)
Paddock married/divorced twice; no kids; good relationship with both ex-wivesNI- (this is weakly inconsistent in terms of Paddock’s not having a history of anger/bitterness in a potentially acrimonious situation)N
First “gun-buying spree” occurred in 2000, one per month Mar-Aug, + Nov; coincided with interest in video pokerNNC (consistent in the coincidence of seeking out greater “strength” (vis-a-vis, protection) through firearms purchases at same time he started gambling career)
Thrifty in appearance and some business practices (involved in construction to save money; did his own books for apartment income rather than pay accountant; worked as on-site manager for a while)NNN
In 2006, which Paddock said was the height of his play, claimed to be “biggest poker player in the world”C (brag)NC (assuming that was indeed his height, his “best days” were behind him)
2011 – Slip and fall at The Cosmopolitan; 2013 – sued for “lingering injury”NC (could contribute to overall angry outburst over failing health)C (concern for age and declining health)
2013 – Moved into first of three 55+ retirement communities at age 60 NNC- (weakly consistent: moving into retirement community at relatively early age [60] could be perceived as disenfranchising, although Paddock was also “thrifty” and retirement communities offer good deals on real estate])
2013 – In relation to deposition for slip and fall, Paddock claimed to have a concealed weapons permit from TXNNC (assumption weapons offer strength; history of seeking strength and self-sufficiency)
2010 – Applied for passport; multiple cruises/international trips until 2016NNC (cousin said he lost interest in travel around 2016)
5/2017 – Internet searches for beaches, sports arenas, hotels, universities, gatherings, et al, in MA, IL, CAN (however appears to speak to lack of solid plan just four months before actual crime)N (however appears to speak to lack of solid plan just four months before actual crime)N (however appears to speak to lack of solid plan just four months before actual crime)
8/2017 – Danley saw uptick in ammo purchases, visits to gun shows and shops, and “unofficial” ranges to practice long-distance shootingN (attack prep, but no insight into motive)N (attack prep, but no insight into motive)N (attack prep, but no insight into motive)
In final weeks before shooting, gambled $160KNNN (not sure where that falls in his normal pattern and if he could afford that kind of expenditure)
9/4-5/2017 – Internet queries for The Ogden, Mandalay Bay, Life is Beautiful, Route 91 HarvestN (just appears to speak to relative lack of long-range planning)N (just appears to speak to relative lack of long-range planning)N (just appears to speak to relative lack of long-range planning)
9/17-28/2017 – Checks into/out of three rooms on three floors at The Ogden; two of the stays occurred during concert dates (9/22-24/2017); one did notN (just appears to speak to poor planning; last minute planning)N (just appears to speak to poor planning; last minute planning)N (just appears to speak to poor planning; last minute planning)
9/18/2017 – After checking into room at The Ogden, flew to Reno; spent night; flew to Phoenix; drove back to The Ogden; immediately departs for Mesquite, NV home; returns to Ogden to check out/check into new roomN (appears to speak to poor planning; last minute planning)N (appears to speak to poor planning; last minute planning)N (appears to speak to poor planning; last minute planning)
Spends week 9/24-30/2017 checking into/out of rooms; driving back and forth to Mesquite four more timesN (appears to speak to poor planning; last minute planning)N (appears to speak to poor planning; last minute planning)N (appears to speak to poor planning; last minute planning)
2004 – Former apartment manager described Paddock as “concerned for tenants’ finances,” “cared about people,” “generous to his tenants” I (seeking infamy via the deaths of others contradicts his apparent “concern and compassion”)I (based on a person’s nature not changing drastically over lifetime)N
Made three reservations for three separate rooms via airbnb between 8/27/2017 and 9/14/2017; on 9/9/2017, Paddock reserved a room at the Mandalay Bay (he made a reservation for a room type, but did not know what floor it would be on)NNN
The Ogden is a condominium complex that allows short-term rentals and has a concierge who passes out keys; the Mandalay Bay is a hotel/casinoN (note: somewhat contradictory to concept of dry run due to the distinction between the two types of dwellings) N (note: somewhat contradictory to concept of dry run due to the distinction between the two types of dwellings) N (note: somewhat contradictory to concept of dry run due to the distinction between the two types of dwellings)
9/2017 – Girlfriend thought trip to Philippines was prelude to break-upNNC (setting aside current life in anticipation of change)
9/17/2015 – Checked into 3 separate rooms at The Ogden through 9/28/2015N (note: could be perceived as covering all bases; could be perceived as disorganized)N (note: could be perceived as covering all bases; could be perceived as disorganized)N (note: could be perceived as covering all bases; could be perceived as disorganized)
“Life is Beautiful” festival ran 9/22-24/2017N NN
9/20/2017 – Queried “Life is Beautiful 2017” festivalNNN
Shot at incendiary fuel tanks (did not ignite)CCC
9/28/2017 – Bought additional rifle; visited gun rangeNNC (guns as conveying feeling of power; sought to restore power up to last days)
Several hundred images of child porn found on his computerNNN
Committed suicide with handgun brought to sceneNNC (control through suicide)
Played video poker proficiently and received quite a few casino perks, but did not appear to be “biggest poker player in world”C (assumption that drove him to seek “achievement” in another way)C (anger at self, directed outward, that he hasn’t achieved what he thinks he deserves to have achieved)C (brag from 2013 deposition, could contribute to dissonance [who he perceives himself to be versus what he has actually achieved])
No physical abnormalities uncovered at autopsyNNC (did not have actual identified physical problems, but believed he had problems)
No brain abnormalities uncovered upon deathNNN
Died without willN N C- (weakly consistent with individual who focused on self)
Paddock made his mom “wealthy”NNN
Sister-in-law had known Paddock 36 years but only saw him approximately 20 times NNN (may speak to family dysfunction, along with Paddock’s isolation and decline)
Family enjoyed perks Paddock received playing at high levels at casinosNNN
Paddock was pragmatic; despite bad things happening “he went on”NII
Brother Eric believed Paddock’s girlfriend was a “gold digger” and expressed anger that she may have access to Paddock’s monetary assetsNNN
Paddock’s mom told sons father was dead after he was sent to prisonNNN
Brother Eric described Paddock boys as “bad” and “troublesome” as youths NC (could speak to aggression that people did not see in the adult Paddock, but may have been present in his youth)N
Only 9 percent of families in 1960 consisted of single parent homesNNN
Eric accused Paddock of tax fraud NNN
Paddock was the “dad” of the family when Benjamin Paddock was incarceratedNNN
Paddock evicted tenants who caused troubleI- (weakly inconsistent in that Paddock appeared intolerant of rule breakers, but then committed major crime himself) I- (weakly inconsistent in that Paddock appeared intolerant of rule breakers, but then committed major crime himself) I- (weakly inconsistent in that Paddock appeared intolerant of rule breakers, but then committed major crime himself)
Paddock checked up on his mom during recent hurricane (two weeks before incident); bought her a walker due to physical challengesNNC (may speak to the way he sees aging)
Only maintained contact with youngest brother (of three brothers)N (non-diagnostic, but contributes to understanding of family dynamics)N (non-diagnostic, but contributes to understanding of family dynamics)N (non-diagnostic, but contributes to understanding of family dynamics)
Brother, Eric, said of other two Paddock brothers, one had “mental issues” and the other was a “sociopath”NC (assuming an element of truth, would speak to family genetics)C (assuming an element of truth, would speak to family genetics)
Brother Eric said long periods would pass without contact with Stephen Paddock; generally only spoke when something “needed to be discussed”N (does contribute to understanding of family dynamics)N (does contribute to understanding of family dynamics)N (does contribute to understanding of family dynamics)
Paddock “always wanted to be the best and known to everyone”CNN
Eric described Paddock as a “narcissist” who “only cared for people who could benefit him in some way”C (in that a narcissist may want to leave behind a legacy)C (consistent in that a narcissist would act in his own self-interest)C (consistent in that a narcissist would act in his own self-interest)
Eric said Paddock “needed to be seen as important” and “needed to be catered to”CNN
Eric believed missing hard drive contained evidence of tax fraud by family (Paddock did taxes for Eric and mother), so the fact it was missing may prove Paddock “did care for us” NNN
Nephew said Paddock was “careful with his money” and planned gambling around opportunities to double or triple points to gain freebiesNNN
No relatives/associates ever saw Paddock angry; girlfriend said he got quiet when mad; brother called him “passive aggressive”; NI (based on accounts of relatives/associates, he didn’t “lash out” when angry C (consistent with basis for anger internal due to lack of control over his health)
Cousin said when Paddock became interested in a subject, he would “devote himself to it and then lose interest” (lost interest in traveling circa 2016)NNC (consistent in that he was losing interest in hobbies [also appeared to be losing edge in poker])
Paddock’s missing/rotted teeth came from inability to go to dentist due to allergiesNNC (pattern of failing health)
Only trivial encounters with law enforcement. I (history of abiding by the law; wide variation from norm)I (history of abiding by the law; wide variation from norm)I (history of abiding by the law; wide variation from norm)

The Analysis of Competing Hypotheses

ACH is an analytical tool whose purpose is to reduce bias. It guides users through the methodical examination of multiple hypotheses side-by-side so as to uncover weaknesses, flaws, and holes in proposed theories. The goal is to reveal those that can be eliminated because they have too many inconsistencies to be valid based on the evidence at hand.

When addressing a new data set or investigative question, the first step is to develop a series of hypotheses through brainstorming that might explain the evidence. It’s not good to settle on a single theory too quickly. First, because new information continues to be generated throughout an investigation. And secondly, because mindsets are easy to reach and tough to shake. Once you’re convinced you have the answer, the tendency is to dismiss evidence that doesn’t fit. This is a mental trap from which recovery can be almost impossible. After you think you’ve thoroughly explored all angles, select a few of the stronger hypotheses to test first.

Now, compile your evidence. This comprises both the tangible and intangible elements of an investigation. For example, in the Route 91 Harvest shooter case, much of the key “evidence” consisted of characteristics interviewees saw in the shooter. Evidence also includes that which is not present, but may be clarifying to the case. For example, that Paddock did not have a presence on social media.

Compile your matrix by placing the initial hypotheses you want to test–three to five is probably easiest to handle at one time–horizontally across the top, and your evidence vertically down the left column. Now, examine each piece of evidence against each hypothesis: no skipping ahead; no “getting back to it later.” Each piece is either “C”(consistent); “I” (inconsistent); or “N” (non-diagnostic), with pluses or minuses if you want to add emphasis. It’s helpful to include comments about why you made the decisions you did.

When you finish your matrix, set it aside. The reason is ACH can be a taxing process. After a break, review your work one or more times. When you’re satisfied, total the inconsistencies of each hypothesis. The ones with the greatest number of inconsistencies can be eliminated. The one with the fewest most closely fits your evidence. If new evidence arrives, you may need to test your theories again, or add new ones.

A few key things to keep in mind:

  1. ACH is a tool. It does not determine the “correct” answer; it identifies weaknesses in hypotheses, thus seeks to eliminate theories that contain too many inconsistencies to support the evidence.
  2. ACH is an element of the investigative process. Ideally, the analyst would present his or her findings to investigators who would use the matrix as an additional tool to guide their investigation.
  3. ACH is subjective. The findings are based on the considered judgment of the analyst or team of analysts/investigators working the case. Robust discussions are common. This is a positive outcome in that it can clarify miscommunications, identify assumptions, loosen/broaden the thinking process, and introduce new ideas.

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