SKOWHEGAN, Maine — The man accused of killing a young mother 31 years ago pleaded not guilty to murder at his arraignment Thursday morning in Somerset County Superior Court.

Jay S. Mercier, 55, of Industry is accused of killing Rita St. Peter, who was found beaten to death off Campground Road in Anson on July 5, 1980. An official cause of death has never been released.

St. Peter was found by a man who was exercising his horses on the dirt road where her body was left, according to a report in the BDN on July 8, 1980. There was no obvious attempt to conceal the body, which reportedly had a substantial amount of blood on it.

State police arrested Mercier on Sept. 28 and charged him with murdering the 20-year-old St. Peter, who had a 3-year-old daughter, Terri Lynn.

He faces 25 years to life in prison if convicted of the Class A murder charge.

St. Peter’s family and friends watched Mercier’s plea in the courtroom on Thursday.

After the arraignment, St. Peter’s sister Christine Belangia read a statement.

“Rita St. Peter was a wonderful person and my sister,” she said. “Rita was adopted by my parents before she was a year old. Being the youngest, I was closer to her than any of the other members of my family. I was 9 when she came to live with us in Anson.

“Rita grew up to be a very smart person. She loved life and enjoyed her friends and good times. The greatest joy of her life was her daughter, Terri Lynn.”

Belangia said that Terri Lynn now has children of her own and Mercier is not her father, contradicting a previous statement by St. Peter’s biological sister Maxine Cross, who thought a Mercier’s motive may have been because he was the father of St. Peter’s daughter.

“After Rita’s brutal murder, July 5, 1980, Terri Lynn continued to live with her grandparents,” Belangia continued. “Soon, due to bad health and [the] age of our parents, Terri Lynn was put up for adoption. Her new family loved her as their own child.

“We would like to thank each and every member of the Maine State Police and others [who] have worked so hard to bring this man to justice,” she said.

Outside the courtroom, Assistant Attorney General Andrew Benson wouldn’t comment on specifics of the case but said the trial date may be as soon as late next spring.

“It is, as you might expect, extraordinarily satisfying [to have a suspect face trial], yet at the same time, because the case is 30 years old, the case has problems that newer cases don’t have,” said Benson, who added that Mercier has been a suspect for quite some time.

“At this point, we felt that the case was never going to get any better,” he said. “Now would be the time to try the case instead of five years from now.”

Belangia urged victims of other cold cases not to give up hope.

“There are cold cases, but don’t ever give up hope because one day, you never know, just like us,” she said. “Just keep your prayers going and keep strong.”

Skowhegan lawyers John Martin and John Alsop are representing Mercier. They did not comment on the case after Thursday’s hearing.

Attorneys have 90 days to make motions in the case.

Mercier is being held without bail at the Somerset County Jail in Madison until a Harnish bail hearing is scheduled at the defendant’s request.