SAN JOSE, Calif. (KRON) — Nearly 50 years after a young teacher was found stabbed to death inside a San Jose high school on the first day of summer break, cold case investigators identified her killer publicly for the first time on Monday.

Branham High School teacher Diane Peterson was stabbed to death by a 16-year-old boy, Harry “Nicky” Nickerson, on June 16, 1978, the Santa Clara County District Attorney’s Office said. Nickerson had a knife with the words, “Teacher Dear,” written on it, investigators said.

One day after the 1977-1978 school year ended, Branham High School teachers were cleaning their classrooms for summer. A student found Peterson lying on the floor near her classroom with a stab wound in her chest.

Investigators cracked the cold case after meeting with Nickerson’s family member this year, according to the DA’s office. Minutes after the killing, Nickerson went to their home and confessed to stabbing the teacher, a family member admitted to police.

“Just this year, investigators learned that he had confessed the killing to a family member. Nickerson committed suicide in 1993,” SCCDAO wrote.

Nickerson was not a Branham High School student, Deputy District Attorney Rob Baker told KRON4. While detectives have never established a firm motive, “detectives at the time theorized that Diane inadvertently interrupted a drug deal on campus the day after school let out for the summer,” Baker told KRON4.

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.”

Nickerson was arrested four days after the killing for an unrelated incident, Baker said. “He spontaneously accused the police of trying to ‘pin’ the murder on him, he denied killing Diane, and denied owning a knife,” Baker told KRON4.

Police took a mugshot of the 16-year-old boy in June 1978, and it bore a strong similarity to a composite sketch based on eyewitness accounts of the high school attack, prosecutors said.

In 1983, a Branham High School student’s family alerted police that their son claimed to have seen Peterson’s violent death and identified Nickerson as the person responsible. The student, however, later denied making that statement. In 1984, another witness told police that Nickerson confessed to killing Peterson, but police were unable to corroborate the claim.

After high school, Nickerson continued committing more crimes, including kidnapping, assault with a deadly weapon, and armed robbery, prosecutors said.

“He was shot and critically injured in 1984 while attempting to commit a drug robbery. Given the circumstances, no charges were filed. He died in 1993 from a self-inflicted gunshot wound,” SCCDAO wrote.

Between 2023 and 2024, the DA’s Crime Lab conducted extensive DNA work on the case in an attempt to identify Peterson’s killer. Unlike other recently-solved South Bay cold cases, forensic investigators were unable to make a DNA match. Instead, the break in the case came from Nickerson’s family member coming forward to police.

“Nearly five decades have passed since a young teacher’s life was tragically taken,” San Jose Police Chief Paul Joseph said. “While the suspect will never stand trial or face the consequences for his actions, 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. No matter how much time passes, we will continue to seek the truth. Every victim matters, and every life deserves justice.”

The DA’s Cold Case Unit was established in 2011 and solved over 30 cold case murders from as early as 1969. The Peterson case is the fourth cold case homicide solved by the DA’s Office in 2025.

A family member of the teacher said, “Diane was a beautiful and wonderful person who is missed dearly.”