CONCORD, N.H. — The New Hampshire Supreme Court ruled Friday that a man convicted of fatally beating an 18-year-old woman more than four decades ago doesn’t deserve a new trial.

Robert Breest has denied killing Susan Randall in February 1971 and tossing her partially nude body onto the frozen Merrimack River in Concord. Breest has twice been denied parole because he refuses to admit to the killing and take part in sex offender treatment.

In its unanimous decision, the court rejected Breest’s request for a new trial and said DNA evidence would not result in a different verdict.

Breest had argued the DNA evidence — three rounds of testing conducted from 2000 to 2008 on Randall’s fingernail clippings — would show Randall had a violent struggle with at least two men. He said that would contradict claims that he acted alone or was one of the killers.

“All four of the DNA tests conducted since 2000 have failed to exclude the defendant as the source of some of the male DNA under Randall’s fingernails, thus further contradicting his position at trial that he had never interacted with Randall and was not in the State when she was killed,” the court said, adding the genetic material was consistent with Breest’s DNA and found one out of 140,000 Caucasians.

The court also dismissed arguments from Breest that he only had to show a new trial would result in a hung jury, rather than an acquittal. It also supported a trial court’s decision to exclude non-DNA evidence that would be available at a new trial, including from a former inmate whom the defense argued would undermine testimony from now-dead convict, David Carita, who said Breest admitted to him that he had killed Randall.

“Consequently, we hold that the trial court’s denial of the defendant’s motion for a new trial was not clearly unreasonable or contrary to the weight of the evidence,” the court said.

Breest’s attorney Ian M. Dumain said they were disappointed with the ruling.