CONCORD, N.H. — A man convicted of killing an 18-year-old New Hampshire woman more than four decades ago has lost his latest attempt to get a new trial.

Robert Breest, 77, claims he was wrongly convicted of beating Susan Randall to death and tossing her partially nude body onto the frozen Merrimack River in Concord in February 1971. He has twice been denied parole because he refuses to admit to the crime and take part in sex-offender treatment. Instead, he has tried to clear his name through DNA testing, as technology and collection methods improved.

In December, the state Supreme Court ordered a hearing on whether he deserves a new trial based on a 2012 test that revealed a second male source of DNA in scrapings taken from under Randall’s fingernails. At that hearing in May, Breest’s attorney argued that those results strongly suggest Randall had a violent struggle with at least two men and contradict the state’s evidence at trial. But in a ruling this week, Merrimack County Superior Court Judge Larry Smukler rejected that argument.

He echoed Assistant Attorney General Elizabeth Woodcook, who had argued that neither the most recent DNA tests nor previous results exclude Breest as the killer. She said the second source of DNA could have been the result of “casual contact” between Randall and someone else or because of contamination during the collection and testing process.

“The most recent DNA test results remain consistent with the state’s theory that the defendant struggled with Susan Randall, received scratch wounds on his hand and then killed her,” Smukler wrote.

Over the years, the DNA evidence has more often pointed to Breest’s guilt rather than innocence, Smukler said.

“If the DNA evidence exonerated the defendant, the outcome of this proceeding would certainly be different,” Smukler said. “This new information, considered in conjunction with the 1973 trial record, would probably not produce an acquittal.”