The murder of Diane Peterson
San Jose, Santa Clara County, California · 1978
Overview
On June 16, 1978, the day after the school year ended, Diane Peterson, an English teacher at Branham High School in San Jose, California, was found on the floor near her classroom with a single stab wound to the chest while teachers were cleaning out their classrooms. A student had heard her calling for help and seen the attacker flee. Four days later police booked a 16-year-old, Harry "Nicky" Nickerson, on an unrelated matter. Prosecutors said his booking photo resembled a composite sketch made from eyewitness accounts; he denied killing her and denied owning a knife. In the years that followed a witness said he had confessed and carried a knife marked "Teacher Dear," a student's family said their son had seen the killing, and another witness said Nickerson had implicated himself, but none of it could be corroborated and he was never charged. He was later convicted of armed robbery, assault with a deadly weapon and kidnapping, and died by suicide in 1993. Extensive DNA work in 2023 and 2024 identified no one. In 2025 cold case detectives asked people close to Nickerson what he had said, and a relative told them he had come to their home minutes after the killing and confessed. On June 2, 2025, prosecutors and San Jose police named him as her killer, 47 years on. He could not be tried.
How it was solved
There was no forensic breakthrough; there was a relative who had kept a secret. Prosecutors said Nickerson was a suspect within days: four days after the stabbing he was booked on an unrelated matter, and his booking photo bore a strong similarity to a composite sketch based on eyewitness accounts. He denied killing Peterson and denied owning a knife. Over the following years, the district attorney's office said, police were told by a witness that Nickerson had confessed and had been seen carrying a knife with "Teacher Dear" written on it; in 1983 the family of a Branham student said their son had seen the killing and named Nickerson, which the student later denied; and in 1984 a witness said Nickerson had implicated himself, saying Peterson had discovered him in a drug deal. Police could not corroborate any of it, and no one was charged. In 2023 and 2024 the district attorney's crime lab did extensive DNA work that never yielded positive results. Deputy District Attorney Rob Baker said there was no sexual assault and only a single stab wound in a public place, so forensic evidence was hard to find. Detectives decided to ask the people closest to Nickerson whether he had made statements to them. In 2025 a relative told investigators that Nickerson came to their home minutes after the killing and confessed to stabbing Peterson. Baker said the statement showed unique knowledge about the crime that could only have come from someone who had spoken with the killer. The office did not charge the relative, saying only that the relative was a witness. Because Nickerson died in 1993, the case closed by official identification rather than a trial.
Sources
- Cold case murder of San Jose teacher solved after 47 years; teen killer had knife inscribed with "Teacher Dear"
“Nickerson was not a student at Branham, Deputy District Attorney Rob Baker said at a press conference Monday.”
- 16-year-old stabbed San Jose teacher to death in 1978, carried knife that read 'Teacher dear:' DA
“Between 2023 and 2024, the DA’s Crime Lab conducted extensive DNA work on the case, but it never yielded any positive results, prosecutors said.”
- Calif. teacher's killing was a mystery for 47 years. Disclosure from relative of student solves it
“The sketch came from a student witness who said they heard Peterson yell for help and saw the killer flee.”
- Cold case solved: High school teacher's killer identified as 16-year-old boy
“"He spontaneously accused the police of trying to 'pin' the murder on him, he denied killing Diane, and denied owning a knife," Baker said.”
- Suspect in 1978 murder of San Jose teacher ID'd as 16-year-old boy, authorities say
“"A student at the time heard Diane calling for help. She was saying help, help, help. That student actually saw the perpetrator flee from the scene," Santa Clara County Deputy District Attorney Rob Baker told ABC7 News on Monday.”
- Teen identified as killer in decades-old murder of teacher
“"The relative did not participate in the killing and did not provide protection or assistance. Just a witness. The relative was emotional and appeared relieved after having kept a secret for almost 50 years," the office said in a statement to ABC News.”
- California teen ID'd as suspect in teacher's 1978 fatal stabbing
“the person provided a detailed statement "demonstrating unique knowledge about the crime that could have only come from someone who spoke with the killer."”
- Student found teacher dead near classroom in 1978, CA officials say. Now, closure
“For decades, the case remained stagnant, and a suspect in Peterson’s killing was never charged.”
- Nearly 50 years ago a teacher was fatally stabbed in a school hallway. A teen who had a knife inscribed with 'Teacher Dear' has been named as the killer
“Investigators from the District Attorney’s Cold Case Unit, established in 2011, reopened the file multiple times.”
- Diane Peterson
“Peterson, who left behind a husband and an infant son, is remembered by her family as a wonderful person whose life was cut short just as her journey in education was beginning.”