Laura Wright 
During the early morning hours of June 2, 2007, something happened outside a small apartment on Linden Street in San Francisco.
Exactly what happened remains uncertain.
What is known is that 36-year-old sound engineer Hugues de la Plaza suffered three serious stab wounds. Blood was found outside his residence and continued inside. De la Plaza apparently made his way through the apartment before collapsing.
When authorities discovered him hours later, he was dead.
The doors were locked.
There was no obvious sign of forced entry.
And perhaps most puzzling of all, investigators could not find the weapon that killed him.
What initially appeared to be a murder soon became something far stranger.
Investigators began considering whether de la Plaza had killed himself.
His family and friends were horrified by the suggestion.
And eventually, investigators from two countries would become involved in determining what happened inside, and perhaps more importantly, outside, the apartment that night.
Who Was Hugues de la Plaza?
Hugues de la Plaza was a French-American citizen living in San Francisco’s Hayes Valley neighborhood.
He worked as a sound engineer and had recently received a promotion. By accounts from those who knew him, he was enjoying his life and career.
On the night of June 1, 2007, de la Plaza went out with friends.
There was nothing particularly ominous about the evening.
He drank, socialized, and eventually left the Underground SF nightclub to walk home.
Surveillance images showed him arriving at his building alone.
He apparently made it safely inside.
Then something happened.
A Normal Evening Turns Deadly
Evidence indicated that de la Plaza did ordinary things after returning home.
He ate.
He used his computer.
Nothing immediately suggested that a violent confrontation had occurred inside the apartment when he first returned.
At approximately 2:38 a.m., however, neighbors were awakened by a disturbance.
One neighbor later described hearing a loud thud and noises involving a door. There were also sounds suggesting someone moving on the stairs and then falling or collapsing.
Nobody knew what those noises meant.
Hours passed.
Then morning arrived.
Blood Outside the Apartment
At approximately 8 a.m., blood was discovered outside de la Plaza’s residence.
Police were called.
Officers could not gain entry through the front, so they went around the building. After seeing additional blood through a window, they forced their way inside.
The scene was disturbing.
There was blood throughout portions of the apartment.
De la Plaza’s body was found inside.
He had suffered three significant wounds.
One was to his abdomen.
Another was to his chest.
The most devastating was a deep wound to the left side of his neck that severed major blood vessels and punctured his lung.
Yet investigators encountered an immediate problem.
Where was the knife?
The Missing Weapon
No weapon capable of causing the injuries was found beside de la Plaza.
Investigators searched the apartment.
There was no knife.
That fact became central to the controversy surrounding his death.
If de la Plaza had taken his own life, what happened to the weapon?
One theory reportedly considered by investigators was that de la Plaza might somehow have disposed of or concealed the knife after stabbing himself.
His family and supporters found that explanation extremely difficult to accept.
A homicide offered a much simpler explanation for the missing weapon.
The killer took it.
But that explanation created another mystery.
How did the killer get out?
The Locked Apartment Mystery
The doors to de la Plaza’s residence were locked.
There was no obvious evidence that someone had forced entry.
At first glance, that seemed to support the possibility that nobody else had been inside.
But it did not necessarily mean de la Plaza had died by suicide.
The blood outside the apartment suggested another possibility.
Perhaps the fatal confrontation hadn’t occurred inside at all.
Was Hugues Attacked Outside?
A reconstruction of the evidence offered a dramatically different scenario.
De la Plaza may have returned home safely, eaten, used his computer and remained inside for some time.
Later, something brought him back to the front door.
Perhaps someone knocked.
Perhaps he heard something outside.
Perhaps he was expecting someone.
Whatever the reason, he opened the door.
The attack may then have occurred outside the apartment.
An independent forensic review later noted blood evidence on an exterior wall that was consistent with blood being cast from the movement of a weapon during a stabbing.
If that interpretation is correct, the locked apartment stops being impossible.
De la Plaza was stabbed outside.
His attacker fled.
De la Plaza retreated into his apartment.
And then he locked the door behind himself.
A Dying Man Inside His Home
Once inside, de la Plaza was losing a tremendous amount of blood.
That may explain some of the apparently strange behavior visible in the crime scene.
Blood smears and handprints suggested a badly injured man attempting to remain upright.
One observer described evidence of de la Plaza gradually collapsing, with bloody handprints and smears descending along a wall as he fell backward.
This interpretation creates a horrifying picture of his final moments.
He may have known he was badly injured.
He may have instinctively locked the door behind him to keep his attacker outside.
Then blood loss began affecting his ability to function.
That could explain why he didn’t telephone emergency services or seek help from his neighbors.
Within a short period, he may simply have been physically incapable of doing so.
But Who Was Outside?
That remains the central mystery.
If de la Plaza was murdered outside his apartment, who attacked him?
There was apparently no clear robbery.
No obvious assailant was identified.
And surveillance evidence did not provide the simple answer investigators needed.
De la Plaza had been out drinking and socializing earlier that night, but nothing about his behavior suggested he believed himself to be in immediate danger.
Someone may have followed him.
He may have encountered a stranger.
He may have opened the door to someone he knew.
Or the attack may have resulted from circumstances investigators never uncovered.
Without the weapon or a clearly identified suspect, those possibilities remained theories.
Suicide or Homicide?
The case became increasingly controversial because de la Plaza’s family and friends strongly rejected the possibility of suicide.
They pointed to his state of mind, his plans for the future, the absence of a weapon, and the physical evidence outside the apartment.
The San Francisco medical examiner ultimately classified the manner of death as undetermined, rather than conclusively declaring either suicide or homicide.
That did little to satisfy de la Plaza’s family.
They wanted the death investigated as murder.
Eventually, they looked beyond San Francisco for help.
France Enters the Investigation
Because de la Plaza was a French-American citizen, his death attracted attention in France.
French authorities became involved, an unusual development for a death that occurred inside the United States.
The French investigation reportedly reached a very different conclusion from the suicide theory.
French investigators believed de la Plaza had been murdered.
The involvement of another country transformed an already unusual San Francisco death into an international controversy.
But another significant development was occurring closer to home.
An Independent Pathologist Reviews the Case
The San Francisco Police Department eventually asked forensic pathologist Dr. Michael Ferenc to review the evidence.
Ferenc examined crime-scene photographs and video, clothing, the autopsy report and other evidence.
His conclusion was remarkably direct:
De la Plaza’s death was a homicide.
Among the evidence Ferenc considered significant was the blood outside the apartment.
He believed some of it was consistent with blood cast from a weapon as it was repeatedly used.
He also identified an injury to de la Plaza’s hand that could potentially have been a defensive wound.
That presented an extraordinary situation.
A forensic pathologist reviewing the case for the police department itself believed de la Plaza had been murdered.
Yet there was still no killer.
Questions About the Original Investigation
Criticism increasingly focused on how the case had been handled during its earliest hours and days.
De la Plaza’s family hired private investigator John Murphy only eight days after the death.
Murphy became convinced that de la Plaza had been murdered and publicly criticized aspects of the police investigation.
Even the original lead investigator, Inspector Antonio Casillas, later acknowledged responsibility for things that should have been done differently.
Casillas explained that the homicide detail was dealing with several death investigations during the same period and resources had to be balanced among them.
But in an unsolved homicide, lost time can be devastating.
Memories fade.
Witnesses become harder to locate.
Physical evidence disappears.
Potential suspects move away.
A mistake made during the first hours of an investigation may never be repairable.
Another Outside Review
The controversy continued after George Gascón became San Francisco’s police chief in 2009.
Gascón made the de la Plaza case a priority and asked the Los Angeles Police Department to evaluate the investigation.
SFPD had also commissioned its own outside medical review, the one in which Dr. Ferenc concluded the death was homicide. The existence and handling of that report became another source of frustration for de la Plaza’s family and supporters.
By then, the case had moved far beyond a simple disagreement over cause of death.
The question had become whether crucial opportunities to solve a murder had already been lost.
The $100,000 Reward
De la Plaza’s parents refused to allow the case to disappear.
His father hired a private investigator and continued pushing authorities for answers.
In 2009, the family offered a $100,000 reward for information leading to an arrest.
Friends also kept public attention on the case through vigils and media appearances.
Their position remained straightforward.
Hugues had been murdered.
Someone knew what happened.
They wanted that person found.
48 Hours Investigates
The unusual circumstances eventually attracted national attention.
CBS’s 48 Hours Mystery devoted an episode, “A Case for Murder,” to de la Plaza’s death in November 2009.
The program examined the crime scene, interviewed investigators, friends and relatives, and explored the conflict between the suicide theory and evidence suggesting homicide.
Television exposure introduced the case to a much larger audience.
It also highlighted what makes the mystery so frustrating.
There isn’t one inexplicable piece of evidence.
There are several.
The Locked Door Isn’t the Greatest Mystery
At first, the locked apartment seems to be the impossible element.
How can someone be murdered inside a residence when the doors are locked and there is no evidence the killer escaped?
But if the attack occurred outside, that mystery largely disappears.
A mortally wounded de la Plaza could have retreated inside and locked the door.
The stranger question is the missing weapon.
If he killed himself, where did it go?
If he was murdered, who attacked him?
Why?
And why was nobody conclusively identified?
The locked-room mystery may never really have been a locked-room mystery at all.
It may have been an unsolved stabbing that happened immediately outside the victim’s front door.
What Happened to Hugues de la Plaza?
The physical evidence ultimately led different investigators toward different interpretations.
But the later independent forensic assessment is particularly difficult to ignore.
Dr. Michael Ferenc reviewed the evidence and concluded that de la Plaza’s death was a homicide. French investigators likewise treated the case as murder.
That still doesn’t tell us who killed him.
Perhaps de la Plaza knew his attacker.
Perhaps he opened the door to a stranger.
Perhaps the encounter began outside and lasted only seconds.
Whatever occurred, the injuries were devastating. De la Plaza apparently made it back inside his home, leaving blood behind him.
Then he locked the door.
Within hours, neighbors discovered blood outside.
Inside was the body of a 36-year-old man whose evening had begun with friends, drinks and celebration.
No murder weapon was found.
No killer was waiting inside.
And nearly two decades later, the most important question remains the simplest.
Who killed Hugues de la Plaza?
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