BURLINGTON, Vt. — A discarded cigarette found near the body of a 24-year-old Vermont school teacher in her apartment nearly 52 years ago helped lead investigators to an upstairs neighbor who they say strangled her after having a fight with his wife, police said Tuesday.

Burlington Police DNA evidence collected from the cigarette butt and dogged investigative work led authorities to the man they say killed Rira Curran within a 70-minute window on a July night in 1971.

The suspect, identified as William DeRoos, who was 31 at the time, had left his apartment that night for “a cool down walk.” After he returned he told his wife of two weeks not to say that he had been out.

Since the investigation was renewed in 2019, detectives re-interviewed DeRoos' former wife, and she told them he had left their apartment for a brief period within a window of time when Curran's roommates were out of her Burlington apartment.

“We’re all confident that William DeRoos is responsible for the aggravated murder of Rita Curran, but because he died in a hotel room of a drug overdose he will not be held accountable for his actions, but this case will be closed,” Burlington Police Detective Lt. James Trieb, the commander of the Detective Services Bureau, said during a Tuesday morning news conference.

After Curran's death DeRoos, who was known to some as a guru, moved to Thailand and became a monk, but he later returned to the United States. In 1986 DeRoos died of a drug overdose in San Francisco, police said.

Curran's parents died without learning who had killed their daughter, but the victim's brother and sister attended the event held at Burlington police headquarters.

“I don't think so much about the guy who did this as I do about Rita, my parents and what they went through," Curran's brother Tom said during the event. “I pray to Rita and I pray to my parents."

In the early morning hours of July 20, 1971 Burlington police were called to the Brooks Avenue apartment after Curran's roommate arrived home to find her body in their shared bedroom.

Police say Curran resisted fiercely, but she was strangled. The murder shook Burlington.

The case remained open and investigators never let it go, but in 2019, Trieb and a team of detectives, officers, technicians and others began working the case as though it had just happened.

A key piece of evidence was a cigarette butt that had been found near Curran's body. In 2014, previous investigators had sent the butt and other evidence off for DNA analysis. The test did compile a DNA profile of whoever had smoked the cigarette, but it did not match any samples in DNA databases compiled by law enforcement.

The detectives who picked up the case in 2019 contracted with a DNA testing company and the samples were compared with genetic material submitted to commercial DNA testing companies by members of the public. Last August, Burlington detectives were told the sample, which had been traced through relatives on both sides of DeRoos's family, was pointing at DeRoos, even though he had no DNA profile on record.

Detectives then determined DeRoos and his wife Michelle had been living upstairs at the time of Curran's death. They had spoken with investigators after Curran's death, but at the time they said they had not seen or heard anything.

DeRoos and his wife, who no longer uses the name DeRoos, left Vermont shortly after Curran's death. Their marriage ended after DeRoos went to Thailand. DeRoos married again after moving back to the United States.

In a recent interview, DeRoos's ex-wife, who lived with him in Burlington and now lives in Eugene, Oregon, told investigators she had lied about her husband leaving their apartment that night. Burlington detectives later interviewed a subsequent wife who told them DeRoos had a penchant for sudden outbursts of violence.

Detective Thomas Chennette, who interviewed DeRoos's first ex-wife, said Tuesday he didn't believe she knew he had killed Curran, but was protecting him because he had a criminal record.

“I think she lied at the time because she was young. She was naive. She was newly married. She was in love," Chennette said.

Now-retired U.S. Sen. Patrick Leahy, who was the Chittenden County State's Attorney when Curran was killed and went to the crime scene that night, attended the Tuesday event. Asked if he felt the case would ever be solved, he said that he had hoped it would.

“I must admit after 20 and 30, 40 years I figured it never would. ... It was a terrible thing," he said.