(Reuters) - DNA evidence from a discarded cigarette butt has led to an arrest in a 31-year-old Maine murder case, in which a young woman was slain after leaving a bar late at night, authorities say.
A laboratory matched DNA from one of suspect Jay Mercier's cigarette butts with sperm found on the body of victim Rita St. Pierre, Maine Deputy Attorney General William Stokes said.
Mercier smoked the cigarette outside his house during an interview with police, who picked up the butt and had it tested, he said.
St. Pierre, 20, was killed after leaving a bar to walk or hitchhike home late on July 4, 1980.
Her partially nude body was found near a road in the small town of Anson, Maine. She had been bludgeoned and run over by a vehicle, according to a state police affidavit.
Mercier, a laborer, was identified as a so-called person of interest after witnesses told investigators they had seen him alone in his truck near the bar when St. Pierre left.
During the initial investigation, although police searched his truck and took prints of its tire treads, they did not find enough evidence to arrest him, the affidavit said.
However, during an interview with a state police detective outside his house in Industry, Maine, in January 2010, Mercier smoked cigarettes, it said. He denied ever meeting St. Pierre or having sex with her, it said.
Police Detective Bryant Jacques gathered one of Mercier's cigarette butts, according to the affidavit.
The DNA match enabled police to get a warrant allowing them to swab Mercier's mouth for more DNA and other tests, Stokes said.
Mercier, 56, entered a plea of not guilty to murder in state court in Somerset County, Maine, on Monday. He was arrested in September and denied bail.
John Alsop, Mercier's court-appointed defense lawyer, has argued for his client to be released pending trial, which is likely to be scheduled for the middle of next year.
"He has been confronted by the police literally from Day One," Alsop said. "He's always denied involvement."
(Reporting by Jacon McLure in Littleton, New Hampshire. Editing by Ellen Wulfhorst and Peter Bohan)