The final moments of Karissa Boudreau's life were revealed in court Friday, as her mother pleaded guilty to strangling her own child with a piece of twine in a grim bid to keep her boyfriend from leaving.

Penny Boudreau, 34, pleaded guilty to second-degree murder Friday in a Bridgewater, N.S. courthouse and was sentenced to life in prison with no parole for 20 years.

Courtroom spectators wept openly as they listened to the brutal details of 12-year-old Karissa Boudreau's murder. They learned that the little girl's last words were "Mommy, don't," as she was pinned down and the rough rope tightened around her neck.

Penny Boudreau left the court silently in police custody, filing through a crowd of reporters who tried unsuccessfully to get her to speak.

Karissa's frozen remains were found on the banks of the LaHave River on Feb. 9, roughly two weeks after she reported her missing on Jan. 27.

Two days after the girl went missing, her mother had made an emotional plea to the media and public to help get her daughter back.

She claimed that the two had an argument in a supermarket parking lot on the day she went missing.

Four months later in June, Boudreau was arrested in Halifax and charged with the first-degree murder of her 12-year-old daughter and only child.

Reading from an agreed statement of facts on Friday, Crown Attorney Paul Scovil revealed chilling, until-now unknown details about the murder.

He read that Boudreau was given an ultimatum by her live-in boyfriend, Vernon Macumber, who told her either the daughter had to go, or he would end their relationship.

According to the statement of facts, Boudreau and her daughter did go to the grocery store on the day Karissa disappeared.

While there, Boudreau left Karissa in the car while she placed a call to her boyfriend, telling him the girl had gone missing.

Boudreau then returned to the car and they drove to a nearby road where she told Karissa to get out of the car. The two then argued, and Boudreau knocked her daughter to the ground before pinning her down and strangling her with a length of twine.

She then dragged the body back to the car, and drove to the nearby river where she rolled the body down the river bank.

On the way she put the twine in a coffee cup and stopped to throw it away, Scovil said.

The statement said the girl's pants came partially off when Boudreau was dragging the body from the car, and she left them in that state to suggest a sexual assault had occurred.

She also put some of her articles of clothing in a garbage at a local swimming pool.

Scovil told the emotional courtroom that Karissa asked her mother to stop.

"Karissa said, 'Mommy, don't,'" Scovil said as people in the public gallery sobbed.

Boudreau stood up and whispered the words "I'm sorry," in the courtroom Friday.

Justice Margaret Stewart, glancing up at Boudreau, told her: "You can never call yourself mother. "The words, 'Mommy, don't.' ... are there to haunt you for the rest of your life."

While the agreed statement of facts confirmed Boudreau's boyfriend had told her it was either him or her daughter if their relationship was to survive, Scovil said there was never any evidence Macumber was involved in the crime.

"Our understanding was that he indicated to her, 'We have to do something within our family, you have to either choose her or me,'" Scovil said outside court.

"We were satisfied he did not mean ... that she was to kill Karissa."

Scovil added that it was clear from the beginning that it was Penny Boudreau, "and her alone, who took responsibility (for) the murder."

Undercover operation

The court was also told Friday of the events leading up to Penny Boudreau's confession of the crime.

In an interview Friday afternoon with CTV Newsnet, Scovil said undercover agents -- posing as members of a crime family syndicate -- were able to gain Boudreau's trust.

On Feb. 14, 2008, Boudreau met with an undercover operative who convinced her that he "could possibly make her 'problem' go away" if she told them exactly what happened.

"She told the undercover operator exactly what happened, and then the next day, led them to (the murder) scene," Scovil told Newsnet from Bridgewater. "Immediately after she had done that, they arrested her and she was taken into custody, and it led to a guilty plea."

When asked why the Crown didn't try to push for a first-degree murder confession, Scovil replied Boudreau's family preferred to settle the legal process now -- instead of waiting what would likely be another year for a higher conviction.

"We took into account the fact that the sentence for first and second-degree (murder) is the same -- it's life," Scovil told Newsnet. Parole eligibility for first-degree murder comes after a minimum of 25 years. "We said we'd need 20 years to accept a second-degree plea," said Scofield.

"In the end, we thought the right thing to do was to take a second-degree with a very high parole ineligibility, and get a conviction."

At the time of the girl's disappearance, police scoured a river and wooded area close to the grocery story, but nothing turned up until passersby stumbled upon the girl's remains.

After an autopsy was performed on Karissa's body, police said they were treating her death as a homicide. They did not release any details about how the girl was killed.

The city of 8,000, about a 90-minute drive southwest of Halifax, hadn't recorded a homicide since 1993.

Residents were stunned by the news of the girl's death.

At Karissa's funeral, Rev. Perry Ingersoll had praised her friendly personality, "winning smile" and love for animals.

Her teachers and friends described Karissa as a typical youngster who liked to sing and listen to pop music.