Man Pleads Guilty to 1973 Murder of a Stanford Law Librarian

“I did not want her to be voiceless and invisible,” she said.

Mr. Getreu, who the authorities now refer to as a serial killer, eluded officers for decades, mostly because DNA-evidence technology used to identify potential suspects was not as advanced as it became, said Michel Amaral, a deputy district attorney in the Santa Clara District Attorney’s Office.

A lawyer for Mr. Getreu, Matt Wilson, could not be immediately reached for comment on Wednesday night.

When Noe Cortez, a detective with the Santa Clara County Sheriff’s Office, re-examined the evidence in 2016, he noticed there was a significant chance to make a breakthrough, Mr. Amaral said.

The attack on her in the desolate woods had been brutal, Mr. Cortez determined from the evidence. Maybe she had scratched the assailant and fought back? Maybe underneath her fingernails, which had been stored and saved as evidence, was leftover DNA of the person who had killed her?

“She really fought hard for her life,” her sister said.

Mr. Cortez submitted the DNA collected from the fingernail clippings to a lab and tested his theory. He received a list of people associated with that DNA. One stuck out, Mr. Amaral said: Mr. Getreu, who, investigators learned, had been convicted in 1964 of raping and killing a 16-year-old girl in Germany. He had been tried as a minor, served a brief sentence and then traveled back to the United States, Mr. Amaral said.

In 2018, after the DNA was analyzed, Mr. Getreu became a prime suspect. That year, detectives were tracking Mr. Getreu and spotted him at a pharmacy in Union City, Calif., about 16 miles northeast of Stanford University, sipping from a Starbucks cup. After he threw the cup away, Mr. Amaral said, investigators retrieved it and used it to collect his DNA. Later, they found that the DNA collected from the fingernails matched that from the cup, Mr. Amaral added.