BLUF | Formal analytical techniques originally developed for use in intelligence analysis are equally effective in crime analysis.
The 2007 death of dual citizen Hugues de la Plaza, who was found in his San Francisco, California, apartment, is unresolved by local authorities with conflicting hypotheses as to whether he succumbed by homicide or suicide. Two entry doors into his unit were locked and bolted, and although his cell phone appeared to be visible and in close reach, he did not seek help. Neighbors reported hearing noise coming from Mr. de la Plaza’s unit around the time of his death, as well as footsteps on the stairs outside, but nothing rose to the level of alerting authorities.
The unusual circumstances of his passing and the lack of a definitive answer by the medical examiner about the manner of death offers an opportunity to apply the Analysis of Competing Hypotheses (ACH), an analytical methodology that can add clarity to ambiguous circumstances. ACH reduces bias by testing multiple possible explanations simultaneously against the evidence at hand. The goal is to identify the hypothesis with the fewest inconsistencies. ACH does not identify a single definitive narrative, per se, but instead, eliminates those with too many inconsistencies to fit the circumstances.
Details
On the morning of 2 June 2007, a neighbor, who shared a porch with Hugues de la Plaza, found blood on the steps leading up to the landing, the landing itself, and on Mr. de la Plaza’s door handle. Upon notification, police arrived and knocked at the front entrance. When they didn’t get a response, they conducted an exterior search of the unit. After seeing more blood from the perspective of a back window, they forced entry. Inside, they found Mr. de la Plaza deceased in the front room. He was later determined to have sustained three stab wounds: one to the left anterior base of his neck; a second to the left breast; and a third to the left upper quadrant of his abdomen. He was also found to have had multiple abrasions and contusions on his head and body, described in the medical examiner’ s report as “blunt force injuries.”
The Medical Examiner’s Register described the crime scene as follows:
“Investigation at the scene revealed the subject, dressed in cut away street clothing and shoes, to be supine in the front room of his apartment. There were copious amounts of frank and partially dried blood on the floor and wall near him. A broken wine glass was noted on the floor of the front room. Bloody handprints were noted on the wall across from the subject. The door to the front room was dead bolted as well as the back door of the apartment where the police forced entry. Blood was noted on the inside door knob and dead bolt as well as the light switch in the front room and adjoining rooms. A blood trail was noted leading from the front room, to the adjoining room, and into the kitchen. Bloody foot prints were noted coming from the front room to the kitchen and leading back to the front room. Three knives were noted in the kitchen as well as an empty bottle of wine. According to investigators from CSI one of these knives appeared to have blood traces on it.“
Additional detail:
- Inside the right pocket of his black denim pants was a bank withdrawal receipt (NFI), $80 cash (three 20-dollar bills, one 10-dollar bill, one five-dollar bill, and five one-dollar bills), a credit card, and other items. Reports are that his wallet was found in his bedroom.
- Reports indicate an overturned TV, and a single broken wine glass at the scene.
- A broken watch was found beneath Mr. de la Plaza’s body. Sources reported the presence of DNA.
- On the coffee table in the front room was a bloodied open laptop computer and a notepad, devoid of apparent blood, with the following two sentences on the visible page: “Learn as if you were to live forever”; and “Live as if you were to die tomorrow.” Some reports said the computer had been disconnected, but other reporting stated it was merely in sleep mode and opened to a pornographic Web site when police tapped the touchpad.
- Mr. de la Plaza’s cell phone had been used to call a friend at approximately 0208 hours on the morning he died.
- Blood ethanol level was 0.11% (w/v); and vitreous humor ethanol noted at 0.10% (w/v). Later tests indicated no drugs were detected in his system.
- During his autopsy, the medical examiner found approximately 10 curly black hair strands from 1/2” to 2″ long adhered to the blood on the left index finger and thumb.
- Mr. de la Plaza was prescribed Viagra around 7 March 2007. He was described by the prescriber as “in good health.”
In terms of the manner of death, the Medical Examiner/Investigator’s Report stated:
“No information has been obtained that elucidates the manner in this case. Although no one has any knowledge of suicidal ideation or attempts by the decedent, the scene is not inconsistent with self-inflicted stab wounds. However, it is not possible to rule out homicide. Therefore the manner will be undetermined.”
Timeline: (Times are approximate, coming from witnesses’ recollections.)
- 1800 (1 June 2007) – Mr. de la Plaza had a date, described both as an encounter arranged on a Web site, and alternatively, with a French woman he met at an art gallery near his home. Reportedly, they drank two glasses of wine. The evening ended amicably.
- (Unknown time) – Mr. de la Plaza returned to his home, went online, called friends and arranged to meet with one along with that friend’s girlfriend at Underground SF.
- 2200 – 2230 – Met up with friends at Underground SF; drank four bourbons (alternatively, three whiskeys).
- 0200 (2 June 2007) – Left Underground SF, walked home. (The route he took is unknown; below are two possible walking routes from Underground SF to his Linden Street apartment. Each would take approximately 10 minutes.)
Used under Google Maps/Google Earth Terms of Service, accessed 12 August 2025
- 0206 – A surveillance camera that was attached either to his building or to an adjacent building, and was situated to capture activity in only one direction on the street, caught him arriving home alone.
- 0208 – Mr. de la Plaza called a friend on his cellphone to set up double date (his friend declined).
- 0214 – Mr. de la Plaza activated his computer and visited 134 Internet sites, 128 of which contained pornography, and Craigslist.
- 0235 – 0238 – Conflicting reports variously state the USB was removed from Mr. de la Plaza’s computer, the power cable was disengaged, or the computer became inactive and went into sleep mode.
- Approximately 0238 – A neighbor heard a commotion, a loud thud, Mr. de la Plaza’s door open and close twice, footsteps running down stairs, Mr. de la Plaza’s door open and close a third time, more footsteps, and another thud.
The Analysis Of Competing Hypotheses:
Step 1: Brainstorm hypotheses that might explain the facts at hand.
- Suicide
- Drug deal gone wrong
- Girlfriend (revenge)
- Money issues (borrowed from the wrong person)
- Targeted hit
- Followed from club
- Dispute with a neighbor (chronic noise complaints/made a pass at significant other/relative)
- Revenge for affair
- Burglary gone wrong (break-in not knowing Mr. de la Plaza was home)
- Passerby (mental illness; impulsive act of violence)
- Mistaken identity (wrong address)
- Problem with someone from work
- Argument with guest
- Home invasion
- Sex worker encounter gone wrong
Step 2A. Construct a matrix and add evidence. Evidence is widely defined. It can be classic forensic material, such as blood patterns and weapons, or lack thereof; facts gleaned from interviews, such as noises heard or not heard; general circumstances, such as weather, day of the week, attributes of a location; and others.
| Blood drops rounded, closely spaced | ||||
| 3 stab wounds (stomach, neck, chest) | ||||
| Just got promotion at work | ||||
| etc… |
Step 2B. Choose initial hypotheses to test–this can be as many as you think you can handle, although too many at one time can be unwieldy. (While it is not always necessary to test every possibility, it was done in this case to ensure the most thorough result.)
| Dispute with neighbor | Girlfriend (revenge) | Sex worker encounter gone wrong | etc… | |
| Blood drops rounded, closely spaced | I (angry dispute would likely result in agitation, thus moving around) | C (familiar person, may reduce agitation) | I (would have been frustrated, moving around quickly) | |
| 3 stab wounds (stomach, neck, chest) | C | C | C | |
| Just got promotion at work | C (potential loud celebration continuing at home) | N | C (sought to hire sex worker to “celebrate”) | |
| etc… |
Step 2C: Working horizontally, fill in your matrix: “C” if the evidence is consistent with the hypothesis; “I” if the evidence is inconsistent with the hypothesis; “N” if the evidence is neutral (non-diagnostic) — it neither supports nor conflicts with the hypothesis. Adding notes in a cell can help you remember your reasoning. You can add a plus or minus sign for evidence you find particularly compelling. Your matrix can be filled out alone or debated among a small group. Decisions are subjective; two analysts may disagree, which is why it’s good practice to add notes. (Analyst’s note: Working horizontally — addressing one piece of evidence and pitting it against each hypothesis — will reduce the bias of favoring a single hypothesis.)
Step 3: Review your matrix, and count inconsistencies. Tally the results at the bottom. The hypothesis with the fewest inconsistencies is the one that most closely fits the evidence currently at hand. Those with too many inconsistencies are less sound, and may be set aside unless additional evidence is uncovered. In some cases, inconsistencies can be helpful in that they point out weaknesses. If they can be resolved through further investigation or newly obtained evidence, they can strengthen a hypothesis. In the following table you will find the inconsistencies counted against each hypothesis in this case.
| Hypothesis | Inconsistencies |
| Sex worker encounter gone wrong | 2 |
| Drug deal gone wrong | 4 |
| Girlfriend (revenge) | 6 |
| Money issues (borrowed from the wrong person) | 7 |
| Targeted hit | 8 |
| Followed from club | 8 |
| Dispute with a neighbor (noise complaint/made pass at wife/girlfriend/relative) | 9 |
| Revenge for affair | 10 |
| Burglary gone wrong (someone broke in not knowing Mr. de la Plaza was home | 11 |
| Passerby (mental illness; impulsive act of violence) | 11 |
| Mistaken identity (wrong address) | 12 |
| Problem with someone at work | 12 |
| Argument with guest | 13 |
| Home invasion | 14 |
| Suicide | 21 |
Step 4: Present and support your findings.
The hypothesis with the fewest inconsistencies pointed to an encounter-gone-wrong with a sex worker, possibly arranged through one of the pornographic Web sites Mr. de la Plaza accessed in the period before his death, or via Craigslist, a site that was also reportedly visited in the period preceding his passing.
Much of Mr. de la Plaza’s activity on the night before he died, his behavior immediately prior to his death, and his lifestyle, generally, appeared to revolve around sexual gratification. Friends who were interviewed said he often scanned the Internet for women; was “dating a new woman every night”; and “just looking for sex.” It was of no consequence if a woman had a boyfriend or a husband, or even if it was the girlfriend of a good friend. An article written in Paris Match stated, “Hugues is a ‘serial dater’ and makes no secret of it. He is a pleasure-seeking anarchist, the kind who gets bored quickly.” Viagra was the one prescription medication found in his apartment, per the medical examiner’s report, although there was no indication whether he needed the drug medically or merely wanted it. The physician who wrote the prescription described him as being in “good health.”
On the night before he died, Mr. de la Plaza had a date with a woman he either met online or else at a local art gallery (sources state both). The date “didn’t go well,” but appeared to end amicably. Later that night, he met friends at Underground SF where he reportedly drank four bourbons (alternatively reported as three whiskeys) and celebrated a promotion at work. Acquaintances said he was enjoying himself and “hitting on girls” hoping, but failing, to meet a woman at the bar. As he departed Underground SF between 0145 and 0200 hours, he joked to friends he was “going to look for a woman to sleep with.”
Shortly after arriving at home, he called a male friend to see if the friend wanted to engage in a double date. However, again, he failed in his quest for female companionship as the friend told him it was late and time for bed. At 0214 hours, he activated his computer, visiting 128 pornographic pages, among 134 pages total, as well as Craigslist, which, at the time, had an Erotic Services section. Then, around 0238 hours, he stopped using his computer.
Step 5: Set forth intelligence gaps (questions to be presented to investigators in hopes of adding insight to the case).
- Did computer or cell phone forensics show contact with an escort service or a similar entity that would have been a means of arranging a sexual encounter?
- Alternatively, were sex workers typically present in the vicinity of the crime around the time it occurred?
- Were sex workers in San Francisco, California, or more widely, known to carry weapons for self-defense?
- Had Mr. de la Plaza used sex workers before? What was his attitude about them? Was Mr. de la Plaza comfortable with the arrangement, or would involvement in illegal activity have made him shameful (hesitant to reach out immediately for medical help)?
- Was the reported DNA on the broken watch ever analyzed? Results?
- Were the black, curly hairs reportedly caught on his fingers ever analyzed? Results?
- Did the security camera that caught an image of Mr. de la Plaza arriving home capture an image of anyone else in the area between 0200 and 0300 on 2 June 2007? (Not arriving with Mr. de la Plaza, as it has been confirmed he arrived home alone, but was anyone else captured on the security camera around the same time?)
Alternative Analysis
Reportedly, Mr. de la Plaza was an “occasional cocaine user.” One source suggested before leaving Underground SF on the morning he died, Mr. de la Plaza asked friends if they knew where he could obtain cocaine. (They did not.) Thus, another explanation for his death, and one with the second fewest inconsistencies, was Mr. de la Plaza may have been a victim of a drug deal gone bad. Again, this would have placed him outside of his unit looking for a dealer. Likewise, he may have hesitated to call 911 due to his participation in illegal activity. Questions here would surround the presence of drug dealers in the vicinity, whether the $80 he had in his pocket was enough to make a purchase, and the openness/shame he may have felt engaging in illicit activity impacting his willingness to reach out to authorities for help.
Both the sex worker encounter gone wrong and drug transaction gone wrong scenarios help shed light on the questions of why Mr. de la Plaza opened his door and walked out to the landing at that hour; and why he did not dial 911.
Select Sources
Medical Examiner-City and County of San Francisco, Medical Examiner’s Register – Record of Death, De La Plaza, Hugues, Case 2007-0642, 4 June 2007, https://www.cbsnews.com/htdocs/pdf/me_report.pdf
Presentation by SFPD homicide inspector Antonio Casillas and forensic pathologist Dr. Venus Azar, National Association of Medical Examiners Conference ( context, https://www.sfweekly.com/archives/s-f-investigators-explain-why-hugues-de-la-plazas-cause-of-death-remains-undetermined/article_dd91dc87-43b1-5f7e-b925-5442b481139e.html), Part I: https://www.youtube.com/watch?v=BEx5-VVNeZI ; Part II https://www.youtube.com/watch?v=qlMFC4TnwM8&t=6s, 26 September 2009
Official Hugues de la Plaza blog: https://huguesdelaplaza.blogspot.com
CBS News, 48 Hours Mystery: A Case for Murder, 19 June 2010, https://www.cbsnews.com/news/48-hours-mystery-a-case-for-murder/
David Le Bailly, Olivier O’Mahoney, Paris Match, “Who Killed Hugues de la Plaza?” 9 January 2009, https://www-parismatch-com.translate.goog/Actu/Societe/Qui-a-tue-Hugues-de-la-Plaza-142124?_x_tr_sl=fr&_x_tr_tl=en&_x_tr_hl=en&_x_tr_pto=wapp
Jaxon Van Derbeken, SF Gate, “Homicide or suicide? Man’s death a mystery,” 1 April 2008, https://www.sfgate.com/news/article/Homicide-or-suicide-Man-s-death-a-mystery-3219748.php (Front of 462 Linden, and interior crime scene)
http://www.realtor.com, accessed 13 August 2025, https://www.realtor.com/realestateandhomes-detail/462-Linden-St_San-Francisco_CA_94102_M22511-22677 462 Linden, San Francisco, California (current)