SKOWHEGAN – When physical evidence in the 32-year-old murder case against Jay Mercier seemed to bog down in court last month with tire tracks and old photographs, the state still had one trick left up its prosecutorial sleeve: DNA.

Investigative work by Maine State Police Detective Bryant Jacques, who collected biological samples from Mercier, and scientists at the State Police Crime Lab in Augusta who analyzed them, allowed prosecutors to convict Mercier of the brutal July 1980 murder of 20-year-old Rita St. Peter.

It was the state’s oldest cold-case homicide.

Even so, it’s not that rare anymore to get a guilty verdict by a jury in such an old case, says Assistant Attorney General William Stokes.

“We’re finding increasing success in some of these old cases,” Stokes said.

Even in the 1980s, investigators took fluid samples from rape and murder victims. Samples from St. Peter’s body were taken and stored during a time when no one had even heard of DNA.

Those samples were enough to send Mercier, 57, of Industry, to prison for 25 years to life. He will be sentenced next month.

“It’s a very satisfying feeling to be able to go to the family of murder victims and to tell them we’ve had a break in the case,” Stokes said. “It’s something that they probably never expected; in some instances, they’ve just given up hope.”

Stokes points to the murder trial of Albert Cochran in 1999, when the Attorney General’s Office got a conviction using DNA samples taken from murder victim Janet Baxter in 1976.

“That was unsolved for almost 23 years,” he said.

There was the case against Thomas Mitchell Jr., who was indicted in September 2006 in the 1983 stabbing death of 23-year-old Judith Flagg in her Fayette home. Like Mercier, Mitchell had been a prime suspect for some time.

DNA found under Flagg’s fingernails was linked to Mitchell. After a jury convicted him, he was sentenced in August 2009 to life in prison without parole.

Walt McKee, an Augusta attorney on the board of the Maine Association of Criminal Defense Lawyers, says DNA evidence can work both ways — it also can clear a suspect of criminal charges.

“I tried a case in Hancock County a couple of years ago where the DNA evidence was really important,” McKee said. “It was obtained, it came back and it was not my client’s DNA. In fact, no DNA was found, which in the context of that case was crucial, and he was found not guilty.”

McKee said DNA evidence in criminal cases changes the game for defense lawyers and how they represent a client. He said it requires lawyers to gain expertise in areas of biological and medical science that most trial lawyers do not have.

“Evidence collection becomes that much more critical, because of the risk of cross-contamination,” he said. “It requires a lot more preparation and it certainly has increased the cost of defending a major case where DNA is involved because of the cost of a DNA expert for the defense to at least review the evidence.”

Maine went online with its first DNA laboratory in August 1997, replacing the science of serology, examining serums and human tissue fluids under a microscope, hoping comparisons with other samples would stand up in court.

Without the genetic profile of DNA, they often didn’t.

Stokes said the Attorney General’s Office now has a prosecutor, Assistant Attorney General Laura Nomani, who works only on cold cases. Nomani worked with Assistant Attorney General Andrew Benson in prosecuting Jay Mercier.

Another prominent murder case in which DNA evidence led to a conviction was that of Edward J. Hackett, who killed Colby College senior Dawn Rossignol of Medway in September 2003. Police used a flake of Hackett’s skin to link him to Rossignol’s car, and in turn to her brutal murder.

Most recently, Juan Contreras of Waltham, Mass., was charged with killing 81-year-old Grace Burton in her Farmington home in June 2010. Contreras was linked to the slaying through DNA. He has pleaded not guilty.

The trial is set for November, and Contreras last week waived his right to a jury trial.

“We’re having more success. Many times it’s the result of DNA technology that helps us, in other cases it’s persistence by law enforcement,” Stokes said.

Detective Bryant Jacques, who ultimately brought Mercier to justice, did so with that same persistence, according to State Police Lt. Christopher Coleman, commander of the Major Crimes Unit North.

Jacques took the first step in the DNA process by taking a cigarette butt Mercier had been smoking during his first interview with him in January 2010 and sending it to the lab for DNA testing.

Mercier’s saliva showed a DNA profile that matched samples taken from St. Peter’s body. He used that evidence to get a warrant for an oral swab from Mercier for more conclusive evidence.

It was a match.

“It was an exciting investigation to work,” Jacques said. “There was a lot of teamwork; there’s a lot of planning involved, a lot of strategy to try to tie up loose ends, to locate witnesses who are no longer available for a lot different reasons.

“There’s a great sense of relief for myself, the department, the family and everyone who was involved working on the case. There’s a lot of relief that justice finally has come forward. It’s something that never goes away, and to hear about how the family felt and to see their expressions of joy was a huge relief.”

Morning Sentinel Staff Writer Doug Harlow can be contacted at 612-2367 or at:

dharlow@centralmaine.com