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A cold case homicide that haunted San Jose for nearly 50 years has finally been solved.

On June 2, 2025, the Santa Clara County District Attorney’s Office announced that 16-year-old Harry “Nicky” Nickerson was responsible for the brutal stabbing. The Branham High School teacher Diane Peterson was murdered in 1978.

Peterson, 25 at the time, was found dead with a stab wound to the chest near her classroom the day after the school year ended. The revelation closes one of California’s oldest unsolved murders. Although justice cannot be served in court, since Nickerson died in 1993 by suicide.

Cold Case Homicide Solved After 46 Years

Nickerson, who was not a student at Branham High School, reportedly confessed to the killing just minutes after it occurred—but only to a family member. That confession did not surface until 2024, when the relative contacted investigators, finally unraveling the mystery.

“This marks the end of a terrible and tragic mystery,” said District Attorney Jeff Rosen. “Ms. Peterson would have been a senior citizen today… I wish she was. I am pleased that we have solved this case, even though the murderer is not alive to face justice.”

In the days following the 1978 stabbing, Nickerson was arrested for an unrelated incident.

At the time, he spontaneously denied killing Peterson and denied owning a knife. Yet detectives now say he carried a blade engraved with the chilling words: “Teacher Dear.”

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The Role of the Cold Case Unit

The Santa Clara County Cold Case Unit, re-established in 2011, played a pivotal role in solving the case. While DNA did not ultimately crack it, unlike many recent cold case resolutions, a family tip provided the key breakthrough.

Since 2011, the Cold Case Unit has solved over 30 murder cases, some dating back to 1969.

In 2021, the unit expanded to investigate cold sexual assault cases after receiving a $500,000 federal grant. So far in 2025 alone, the unit has resolved four cold case homicides and five sexual assault cases.

“No matter how much time passes, we will continue to seek the truth,” said San Jose Police Chief Paul Joseph. “Every victim matters, and every life deserves justice.”

More on the Cold Case Unit: Santa Clara County Cold Case Unit

A Life Lost Too Soon

A family member remembered Peterson as “a beautiful and wonderful person who is missed dearly.” She had stayed in her classroom to clean when she encountered Nickerson.