A French inquiry has declared the 2007 stabbing death of a French national in San Francisco to be a homicide, an apparent challenge to San Francisco police investigators who have yet to declare the case a slaying and suggested the man stabbed himself to death in his apartment.

The family and French government are now offering a $100,000 reward for information in the June 2, 2007, death of 36-year-old Hugues de la Plaza.

Although police labeled the case as a possible homicide, they also angered de la Plaza's family and friends by indicating he may have killed himself.

French Judge Brigitte Jolivet came to San Francisco in June to oversee the unusual French probe into the local case, summoning witnesses and reviewing evidence that had been gathered by San Francisco homicide inspectors. San Francisco police cooperated with Jolivet's inquiry.

Homicide investigators defended their ambiguous findings by pointing out that the chief medical examiner's office was unable to determine whether de la Plaza was a homicide or suicide victim. But two forensic experts who examined de la Plaza's autopsy photos and findings for the French inquiry concluded he had been killed, said Melissa Nix, a one-time girlfriend of de la Plaza who has been critical of how police handled the case.

The French probe "declared it a homicide, without a measure of a doubt," said Nix, who said she was notified of the findings of the French probe by de la Plaza's father, who met with the judge and investigators this month.

San Francisco police Lt. Mike Stasko, the head of the homicide detail, said his investigators had been informally told of the French finding last week. But, he said, his investigators have yet to see the official report and are going through the protocol of formally requesting it from the French government.

"I have been told that they have concluded it is a homicide, but I don't know what they're basing that opinion on," Stasko said. "We're willing to see what they have and act on it."

De la Plaza's body was found inside his locked apartment on Linden Street in Hayes Valley. Police first said he may have stabbed himself after ingesting drugs, but no bloody knife was recovered and no drugs were found in his system.

A knife was found in the sink area and appeared to be stained red, but an examination by police forensics experts found the red was from tomato sauce, not blood.

Police suggested that de la Plaza had stabbed himself with the knife and then washed it, a theory derided by his family and friends.

They said de la Plaza, a sound engineer who held dual U.S. and French citizenship, had been making plans to move to Argentina and had given no hint he was depressed or suicidal. An acquaintance filed a complaint last March with the city's civilian-run police watchdog agency, the Office of Citizen Complaints, saying lead inspector Antonio Casillas and other investigators were willfully ignoring evidence of a homicide and had conducted an inadequate probe.

Investigators said a surveillance video that provided partial coverage of de la Plaza's apartment showed him returning home from a nightclub early the morning he died, but no one else entering.

No suicide note was found, but de la Plaza had written on a notepad, among other things: "Learn as if you were to live forever," and, "Live as if you were to die tomorrow."

Friends of de la Plaza, led by Nix, have mounted a campaign and worked with de la Plaza's family in France to persuade San Francisco police to conclude the case was indeed a homicide.