CARIBOU, Maine — A Superior Court jury deliberated for 2½ hours Wednesday before finding baby sitter Heather Fortin not guilty of manslaughter in the death of 20-month-old Teairra Leathers last year.

Fortin, 25, of Limestone, gasped, fell into the arms of a male friend and began to cry when the jury forewoman gave Justice Kevin Cuddy the verdict shortly before 4 p.m., concluding the two-day trial.

“Justice is served,” Fortin’s attorney, Jon C. Gale, said after the jury’s decision.

“There were a number of problems with the state’s case,” Gale said. “In the beginning, they worked under the belief that the evidence would show that my client committed the crime and so [the state] failed to satisfactorily investigate other suspects.”

Fortin declined to comment. The baby’s mother, Rena Leathers, was in court but left before she could be interviewed.

Assistant Attorney General Andrew Benson conceded that his case was flawed.

“We always said it was going to be extremely difficult to get a conviction because the case was based entirely upon circumstantial evidence,” Benson said after the verdict.

Fortin was indicted for manslaughter nine days after accepting 20-month-old Teairra into her care for the evening of June 18, 2007, while her friend Leathers and Leathers’ then-boyfriend, Shayne Ellis, attended a Narcotics Anonymous meeting in Caribou.

According to Fortin and several witnesses who testified, Fortin called 911 within 15 minutes of receiving Teairra at her Huggard Avenue house because the little girl had gone limp and was struggling to breathe. Teairra Leathers died a day later at Eastern Maine Medical Center in Bangor.

State police arrested Fortin on June 27 and charged her with manslaughter. She pleaded not guilty and spent an undetermined amount of time incarcerated at the Aroostook County Jail before being released on bail.

State police never believed the story offered by Fortin and her friends, Benson said. They claimed that at first the baby was happy and lively and cooperative, even cheerful when Fortin changed her, but lapsed into mysterious unconsciousness almost immediately afterward.

State Deputy Chief Medical Examiner Dr. Marguerite DeWitt and pediatric neurologist Dr. Stephen Rioux of Portland testified that Teairra’s apparent injuries — blunt trauma to her head — would have forced unconsciousness upon her within five to seven minutes of their occurrence, Benson said.

But Gale said he elicited further evidence during his cross-examination.

“In essence, neither of the physicians could say that the medical evidence proved that the injuries to the child occurred while Heather Fortin cared for the child,” Gale said.

Nor were there any witnesses to any malfeasance on Fortin’s part, or anything in Fortin’s past, Gale said, that indicated she could harm a child.

Also, key witness Elizabeth Ellis reversed her testimony, Gale said. The grandmother of Leathers’ ex-boyfriend, Ellis had told state police that the baby was cheerful and sat in an infant’s car seat during the car ride to Fortin’s house.

But under cross-examination, Ellis said that the baby was unusually quiet and sat wrapped in a blanket in her mother’s lap during the ride, Gale said.

“The doctors also testified that they were unable to determine whether the child died from blunt trauma, shaking, or a combination of the two,” Gale said.

The verdict will likely leave Teairra’s death a mystery, Benson said.

“We have prosecuted the one person against whom we had any evidence,” he said. “There is no evidence pointing to any other person.”