BANGOR – Pointing to botched ballistic evidence and another man’s confession, attorneys for convicted murderer Jeffrey Cookson on Friday made their final arguments for a retrial.

“How could a conviction of murder possibly stand when the key piece of evidence turns out to be false?” Cookson’s Auburn attorney, William Maselli, asked Justice Roland Cole in Penobscot County Superior Court, where onlookers entered the courtroom under heightened security due to the case’s notoriety.

Late last year, a jury deliberated for 13 hours before finding Cookson, of Dover-Foxcroft, guilty in the 1999 execution-style slayings of his estranged girlfriend, 20-year-old Mindy Gould, and 21-month-old Treven Cunningham, whom she had been baby-sitting at a Dexter home.

On Friday, Maselli said a new trial was warranted because during the original trial, Maine State Police firearms experts offered erroneous testimony linking Cookson to a gun prosecutors said was used to kill Gould and the toddler.

That testimony was crucial to Cookson’s conviction.

In a bizarre twist after the December 2000 verdict, another man, 21-year-old David Vantol of Bangor, led police to the hiding place of the real murder weapon – and offered a videotaped confession to the crime.

Vantol later recanted his confession, testifying that Cookson had coached him on the details of the crime – including the gun’s hiding place – and offered to pay him for taking the blame.

In his arguments before the court, Maselli argued that detectives had pressured Vantol into changing his story.

While Assistant Attorney General Fernand LaRochelle acknowledged the ballistics error – blaming it on an inexperienced firearms examiner – he emphatically denied defense claims that authorities allowed the true murderer to go free by not arresting Vantol.

“If I believed in my heart that Vantol killed those two people, he wouldn’t be walking the streets,” said LaRochelle, a veteran prosecutor who discounted the confession from the man who has a history of mental illness and a limited education.

Despite his conviction, Cookson, 39, has not yet been sentenced in the case, pending the outcome of his retrial request.

Cookson has remained behind bars since his arrest a few weeks after the murders.

Cole is expected to issue his decision on the retrial motion in the next few weeks. Regardless of how Cole rules, the case likely will go to the Maine Supreme Judicial Court for review.

On Friday, Cookson, slouched in his chair, sat silently during most of the morning proceedings, occasionally passing hastily written notes to his attorney.

Friends and family of Gould and Cunningham watched sternly as Maselli blasted the state for not “biting the bullet” and conceding to a new trial considering the “incredibly recklessly false” testimony of the firearms experts.

LaRochelle spurned Maselli’s rebuke, instead chastising the defense attorney for not hiring his own ballistics expert to examine the evidence.

“If you don’t do your homework, you can’t point your finger at the state and blame them,” said LaRochelle, who called the retrial request an attempt to “pull a rabbit out of the hat” after the guilty verdicts.

The victims’ friends and family members reserved comment on the case pending Cole’s ruling, with a family spokesman saying only that he was certain of Cookson’s guilt.