On June 2, 2025, the Santa Clara County District Attorney’s Office and the San Jose Police Department announced that the 1978 murder of 26-year-old English teacher Diane Peterson had been solved. The case had gone cold for 47 years. Harry Nickerson, a 16-year-old who was questioned days after the killing but never charged, was identified as the killer. He died by suicide in 1993 at age 31, so no arrest was ever possible.
Diane Peterson taught English at Branham High School in San Jose, California. She was married and had an infant son. In the final weeks of the 1978 school year, she was told her position was being cut due to declining enrollment, but she continued showing up to finish the year. On June 16, 1978, the day after the last day of school, Diane was in her classroom recording final grades.
Someone walked in and stabbed her once in the chest. She ran about 70 yards into the main hallway, calling out for help, before collapsing. She was rushed to Good Samaritan Hospital and pronounced dead. A student heard her cries and saw a young man running away.
There was no robbery—her purse was untouched—and no sign of sexual assault. Investigators had almost no physical evidence: no weapon, no defensive wounds suggesting a prolonged struggle, and no useful trace evidence. A composite sketch was drawn from the witness description. Four days after the murder, police arrested 16-year-old Harry Nickerson on an unrelated charge.
His booking photo bore a striking resemblance to the sketch, and he became the prime suspect. During questioning, Nickerson spontaneously denied killing Diane and denied owning a knife, before investigators had laid out a case against him. But in 1978, without DNA testing or physical evidence tying him to the scene, there was not enough to charge him. Nickerson, who dropped out of school in the eighth grade and was known for a violent temper, built a long criminal record after the murder.
In 1984, he was shot and left paralyzed during a botched armed robbery. He died by suicide on August 31, 1993. Over the years, leads came and went. In 1983, a student’s parents claimed their son had witnessed the killing and identified Nickerson, but the student denied it.
A separate 1984 tip claimed Nickerson had been seen carrying a knife inscribed with the words “Teacher Dear,” but it could never be corroborated. Between 2023 and 2024, the Santa Clara County District Attorney’s Crime Lab conducted extensive DNA testing on surviving evidence. The results came back inconclusive, with the degraded evidence too thin to build a case on. Earlier in 2025, a relative of Nickerson came forward and told investigators that Nickerson had confessed to stabbing Diane Peterson minutes after the killing.
Deputy District Attorney Rob Baker said the relative’s account contained specific, unique knowledge about the crime that could only have come from someone who had spoken directly with the killer. The account matched existing evidence: the timeline, the detail about the inscribed knife, Nickerson’s build, and his resemblance to the composite sketch. Investigators said the relative was visibly emotional during the interview, relieved to finally set down a secret carried for almost 50 years. The District Attorney’s Office did not file charges against the relative, saying it was reasonable to assume the decades of silence came from fear of retaliation, not indifference.
At the June 2025 press conference, District Attorney Jeff Rosen said: “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.
I am pleased that we have solved this case, even though the murderer is not alive to face justice. I wish he was. ”
San Jose Police Chief Paul Joseph said, “Nearly five decades have passed since a young teacher’s life was tragically taken. ” A member of Diane’s family, who asked not to be identified, thanked investigators, saying, “Diane was a beautiful and wonderful person who is missed dearly.
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The case was closed with certainty but without a trial, conviction, or punishment. Nickerson never spent a day in custody for the murder. San Jose’s cold case unit has now solved more than 30 homicides dating back to 1969. Diane Peterson was 26 years old.
She is remembered as a teacher who continued showing up to her classroom even after being told she would lose her position, until the very last day she was given.