SKOWHEGAN — Fading memories, lost witnesses and decades-old forensic evidence will be among the challenges in a 32-year-old murder case set for trial this week.

Jury selection will begin Wednesday in the trial of Jay S. Mercier in one of the state’s oldest cold-case homicides.

Mercier, 57, of Industry, is charged in the 1980 murder of 20-year-old Rita St. Peter of Anson. Her body was found off Anson’s Campground Road on July 5 that year. She had been beaten, her skull was fractured, and police said she appeared to have been run over by a car or a truck.

St. Peter’s death left her 3-year-old daughter without a mother.

Mercier had been a suspect from the beginning, state police investigators said last year when he was arrested after they said his DNA matched evidence found at the murder scene. He later was indicted on a single count of murder by a Somerset County grand jury.

He has been held without bail since then.

Tire marks from Mercier’s pickup truck were inked and printed the day after St. Peter was found, but it wasn’t until December 2005 that a forensic scientist matched the impressions to those from the crime scene, according to court documents.

Skowhegan defense attorney John Alsop, one of two lawyers representing Mercier, said he would not comment before trial on the state’s forensic evidence. Alsop previously has said that he wants to know why the tire impression evidence was not completed until 25 years after the crime.

He said the trial will be a challenge both for the prosecution and the defense.

“The case is 32 years old and there are a lot of unanswered questions,” Alsop said. “There seems to be a lot of missing evidence; there’s a lot of witnesses that are no longer available. There are a lot of failures of memory and the types of things you’d expect from a very old case. Those are challenges.”

Mercier may have been a suspect from the beginning, Alsop said after a bail hearing last year, but he never has confessed to the crime, and there were many other suspects over time. While there is evidence of sexual contact, Alsop questioned whether there is evidence showing when the contact took place.

Assistant Attorney General Andrew Benson, who is prosecuting the case, said during the bail hearing last year that there is evidence Mercier sexually assaulted St. Peter, bludgeoned her on the head with a weapon similar to a tire iron and partially ran her over with his pickup truck.

Alsop insisted that sex does not prove Mercier killed St. Peter.

Mercier is divorced, has been employed as a laborer most of his life and was living with a girlfriend at the time of his arrest, police said.

St. Peter was last seen alive around midnight July 4, 1980, near the bridge connecting Madison and Anson. She had been at a Fourth of July party and stopped at the former Depot Tavern in Madison for a nightcap.

Two witnesses told police they had seen Mercier in his truck outside the bar around the same time. Alsop has said that because Mercier lived a few blocks from the bar, it would not be unusual that he would be seen in downtown Madison.

St. Peter’s body was found face up on a field road the next morning. Her clothing was ripped and her face, her head and the ground were covered in blood, according to a court affidavit.

The day after St. Peter’s body was found, Mercier signed a consent form to allow police to search his 1980 GMC pickup, the affidavit states.

Motions to suppress Mercier’s statements to investigators that year, and later in 2010 and 2011, and to exclude evidence gathered in the search of the truck were denied in a ruling filed June 25 in Somerset County Superior Court

Alsop said he expects the trial to begin Thursday and to last more than a week. Justice John Nivison will hear the case.

Mercier remains at the Somerset County Jail in East Madison. He faces 25 years to life in prison if convicted.

Doug Harlow — 612-2367

dharlow@centralmaine.com