SAN JOSE — A family member’s recent confession has definitively linked a long-former Branham High School student to the fatal stabbing of a teacher near her classroom almost five decades ago, authorities announced Monday.
Diane Peterson poses in an undated photo. She was stabbed to death near her classroom at Branham High School in San Jose in 1978, and in June 2025, her killer was officially identified as a then-16-year-old student who had been suspected but could not be definitively linked to the death. The student, Harry "Nicky" Nickerson, died in 1993. (Photo courtesy of the Peterson family via Santa Clara County District Attorney's Office)A renewed investigation by the Cold Case Unit at the Santa Clara County District Attorney’s Office, alongside San Jose police, has led to Harry “Nicky” Nickerson being identified as the presumed killer of Diane Peterson on June 16, 1978.
Nickerson died by suicide in 1993, following a troubled post-school life that included multiple run-ins with law enforcement and an earlier gunshot injury stemming from his documented criminal activity.
“This marks the end of a terrible and tragic mystery. Ms. Peterson would have been a senior citizen today if she had not crossed paths with this violent teenager. I wish she was,” District Attorney Jeff Rosen said in a statement. “I am pleased that we have solved this case, even though the murderer is not alive to face justice. I wish he was.”
Peterson, 26, was found dead from a single stab wound to her chest at the South San Jose campus; school had let out the day before, and faculty and staff were cleaning out their classrooms for the summer break.
A Branham student who claimed to have witnessed the killing helped San Jose police produce a sketch of a suspect, who roughly resembled a then-16-year-old Nickerson, but the student did not directly implicate him. That witness’s parents later contacted police to report their son told them that Nickerson was indeed the attacker, but when interviewed by detectives the student reportedly denied the claim.
At left, police in 1978 released a sketch of a suspect in the stabbing of teacher Diane Peterson at Branham High School. At right, Harry "Nicky" Nickerson poses in an undated photo. In June 2025, authorities officially identified Nickerson as Peterson's killer. Nickerson died in 1993. (Santa Clara County District Attorney's Office)The Cold Case Unit, which revisited the case in recent years, said Nickerson also drew suspicion on himself about a month after the killing, when he was arrested in San Jose for an unrelated matter. During an ensuing interrogation, Nickerson — reportedly unprompted — accused police of “trying to pin the murder of Peterson on him.”
So while Nickerson was on their radar, authorities did not have any direct evidence linking him to Peterson’s death. They thought they might have had a break in the case in 1984 when a man described as a criminal associate claimed Nickerson confessed to killing Peterson and suggested the motive was her witnessing him taking part in a drug deal.
In the years after the killing, Nickerson ran afoul of the law with arrests and convictions for assault with a deadly weapon and kidnapping; in 1984 he was shot and seriously injured during an attempted drug robbery. The associate who talked to police — and later passed a polygraph test — also reportedly said Nickerson carried around a knife with the phrase “Teacher Dear” inscribed on it.
Police could not independently corroborate the associate’s claims, so Nickerson was not arrested or charged.
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Those efforts were exhausted earlier this year. The DA’s office said that prompted its Bureau of Investigations to make a last-ditch effort to find Nickerson’s surviving relatives for any new information. That search effort, led by DA Investigator John Cary — a former veteran SJPD detective — eventually located a family member, who reportedly admitted that “Nickerson came to their home minutes after the killing and confessed to having stabbed Peterson.”
In a statement released through the DA’s office, a relative of Peterson’s who asked to be unnamed lauded investigators for “not giving up for 47 years,” and said that “Diane was a beautiful and wonderful person who is missed dearly.”
San Jose police Chief Paul Joseph said in a statement that while there will be no trial for Peterson’s death, “we hope this resolution brings a measure of peace to the victim’s loved ones and to a community that has carried this loss for far too long. Let this serve as a solemn reminder: no matter how much time passes, we will continue to seek the truth — because every victim matters, and every life deserves justice.”
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