A man who lived two floors above Rita Curran in the same Brookes Avenue apartment building killed the 24-year-old teacher more than 50 years ago, Burlington police announced Tuesday.

Sophisticated DNA technology in labs from New York to Florida ultimately led detectives to William DeRoos, who police say left a cigarette butt at the scene of Curran’s murder on July 19, 1971. That piece of evidence was later analyzed by a genetic genealogist who matched DNA from descendants of DeRoos, who died in 1986 in San Francisco at age 46 of a drug overdose.

Burlington Police Acting Chief Jon Murad said DeRoos, who was 31 at the time, had just gotten married. The night Curran was killed, DeRoos and his wife argued, and DeRoos left the apartment for what Murad called a “a cool-down walk.”

The next morning, when questioned by detectives investigating the murder two floors below them, DeRoos and his wife said they had spent the night together in the apartment and didn’t hear or see anything suspicious.

Tom Curran, brother of 1971 murder victim Rita Curran, faces reporters during a news conference at the Burlington Police Department (AP Photo/Wilson Ring).

Five decades later, Murad said, DeRoos’ former wife “told our detectives a different story — the truth.” She told detectives that her husband had left their apartment for a brief period when Curran’s roommates were out.

Murad heaped praise on officers and investigators who have worked the case through the years. He singled out Detective Lt. James Trieb, commander of the department’s Detective Service Bureau. Murad said Trieb reopened the case a few years ago and decided to create a team that would treat cold cases as if the crimes had just been committed.

“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,” Trieb said.

Curran’s parents died before justice could be served for their daughter. But Murad said her family, included Curran’s siblings, Tom Curran and Mary Campbell, were informed of the DNA evidence at a luncheon last week.

“I don’t think too much about the guy who did this as I do about Rita and my parents, and what they went through,” Tom Curran said at Tuesday’s press conference.

Campbell said her sister’s legacy will always be remembered by her family. “This is our case, and this is our sister, and she’s always with us. We now have two generations in our family who never knew her,” she said.

Campbell noted that the cold-case organization ‘Season for Change’ donated to the Burlington Police Department to improve their DNA testing capabilities. Curran’s family has set up a GoFundMe for the group to show gratitude to their role in bringing justice to Rita Curran.

“She was a teacher, a singer and a giver and she was loved,” Murad said. “And the random violence of her murder left a stain on our community and it devastated her family and for 50 years they have waited for justice.”

The Associated Press contributed to this report.