SKOWHEGAN — DNA samples taken from murdered 20-year-old Rita St. Peter in 1980 match the DNA profile of Jay Mercier, of Industry, the man accused of sexually assaulting and killing her, a state witness said in court Monday.

“Unless you have an identical twin, there is no one else in the world with your DNA,” Kathy MacMillan, a forensic DNA analyst with the state police crime lab told a jury in Somerset County Superior Court.

MacMillan said the possibility of samples taken from St. Peter’s body and from a swab sample from Mercier’s mouth taken by Maine State Police in 2005 not belonging to Mercier is one in a trillion.

“Those are identical matches with Mr. Mercier?” Assistant Attorney General Andrew Benson asked her.

“That is correct,” MacMillan answered.

MacMillan’s testimony came during the third day of the murder trial of Mercier who was 25 when St. Peter’s body was found off Campground Road in Anson July 5, 1980.

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

St. Peter was last seen alive around midnight July 4, 1980, walking toward 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 the jury last week they had seen Mercier in his truck outside the bar around the same time. Mercier’s defense team 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.

Skowhegan attorneys John Alsop and John Martin have told the jury that DNA evidence may prove that Mercier and St. Peter had sex, but it doesn’t prove he killed her.

Prosecutors say Mercier, now 57, had sex with St. Peter, beat her with something like a tire iron, then ran her over with his truck.

The state’s chief medical examiner testified Monday morning that St. Peter died as a result of blunt impact injury to the head and chest.

Dr. Margaret Greenwald said the autopsy report by then-Chief Medical Examiner Henry Ryan in 1980 showed that a long, heavy object was used to kill St. Peter.

Benson and his co-counsel, Assistant Attorney General Laura Nomani, also have presented evidence in court showing tire prints taken from Mercier’s truck the day the body was found match tire prints photographed at the scene of the murder. Alsop has pointed out that several different types of trucks could have had the same tires on them that year.

While Mercier had been a suspect in the St. Peter murder and the case has remained open for 32 years, Benson said state police Detective Bryant Jacques struck “forensic gold” in 2005 when he took the butt of a cigarette Mercier had been smoking and turned it over to the crime lab.

DNA testing on the cigarette butt matched samples taken from St. Peter, allowing police enough probable cause to get a search warrant in 2011 for a swab from Mercier’s mouth.

Investigators in 1980 collected samples of fluid from St. Peter’s body, but testing at the time could not test for DNA. The samples were marked and stored and were used as evidence Monday in the case against Mercier. Police in 1980 also kept St. Peter’s clothing, a section of which also was tested and found to contain traces of semen.

Steve Shargo, a forensic chemist with the crime lab, told the jury that stored evidence was sent for chemical testing in 2009. Evidence included two glass, smear slides containing fluid samples taken from St. Peter’s body. He said more than 50 sperm cells were found in one sample.

“We need 10 cells to get DNA,” Shargo said. “We found over 50, making it a fair number of cells.”

Shargo said underwear taken from St. Peter’s body was damaged and more sperm samples were found on sections of the underwear.

Skin samples taken from the inside waistband of St. Peter’s underwear also revealed male DNA, but not in amounts sufficient to tie them to Mercier, Shargo said.

He also said her blue jeans were torn apart along the vertical seam from the waistline to the crotch.

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

The trial continues today.

Doug Harlow — 612-2367

[email protected]

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