A transgender teenager has pleaded guilty to killing her parents and dog on Halloween because they wouldn't accept her transition.

Andrea Balcer, who is still referred to as Andrew Balcer in court documents, sobbed in court as the prosecutor described how she had stabbed Alice and Antonio Balcer, both 47, to death on October 31, 2016.

The 19-year-old also fatally stabbed the family's chihuahua but spared her brother's life.

Andrea Balcer, who is still referred to as Andrew Balcer in court documents, sobbed in court as the prosecutor described how she had stabbed Alice and Antonio Balcer, both 47, to death

The teen did not give any explanation for the horrific murders in court.

But Balcer's attorney, Walter McKee of Augusta, said outside court that his client had been sexually abuser by her mother as a teenager.

He added that Balcer's parents had struggled to accept her transition into a transgender woman.

'She has indicated some issues with respect to transitioning from the gender assigned at birth [as a trigger for the crimes],' he said.

But Assistant Attorney General Robert 'Bud' Ellis has dismissed Balcer's abuse claims.

'Our position is basically that we do not accept that as reality,' Ellis said outside court.

The 19-year-old also fatally stabbed the family's chihuahua but spared her brother's life

The teen did not give any explanation for the horrific murders in court (pictured being led away after pleading guilty)

Dr. Debra Baeder, Maine's chief forensic psychiatrist, testified last year that Balcer was afraid her parents would not accept her as she transitioned.

Baeder held several sessions with the teen after the murders.

In one session, she said Balcer told her: 'Maybe I should be someone else. Maybe, I should be a woman.'

'I couldn't be as flamboyant as I wanted. I couldn't dress the way I wanted,'' she testified Balcer told her.

In court last year, a recording of Balcer's 12 minute call to 911 revealed her confessing to stabbing his mother in the back while she was hugging her, before stabbing his father when he woke up from the screams.

A military-style knife was found stuck in the floor near her father's body.

'I took my Ka-Bar (knife) and drove it straight into my mother's back,' Balcer told the dispatcher after murdering her parents October 31, 2016.

Balcer and her mother Alice are shown. School officials said they saw no indication of violent behavior from Andrea, who was a student at Winthrop High School at the time

Mr Balcer became an ordained reverend after he retired from the US Coast Guard

'My father came up because he heard her screams and I stabbed the f**k out of him.'

She said she stabbed the dog because it would not stop barking.

Alice Balcer was stabbed nine times and Antonio Balcer was stabbed a dozen times, according to the autopsy report.

Balcer, who was just 17 at the time of the stabbings, also said on the recording that she did not know why she did it, and that there had not recently been arguments with her parents.

'There's no helping them,' she said on the tape.

Prosecutors filed a petition to have Balcer tried as an adult which would have meant an automatic life sentence under Maine law.

Andrea Balcer, now 19, and Alice on a 2014 trip to Italy. Balcer is charged with double murder for stabbing her parents Alice and Antonio Balcer

The teen was charged with double murder for stabbing Antonio and Alice Balcer (pictured together) to death in their Winthrop home last Halloween

This week, Balcer pleaded guilty to two counts of intentional or knowing murder and one count of aggravated cruelty to animals as part of a plea agreement with the Maine attorney general's office that calls for the prosecution to recommend 55 years in prison.

McKee is free to argue for less time in prison.

Balcer, who has been held without bail since the 2016 murder, will be sentenced in November.

The superintendent of Winthrop High School, where Balcer attended school at the time, previously told Central Maine school he saw no 'tell tale' signs of violent behavior from her.

'From what best I know, he was a very good kid, a very good student, an academically superior student,' Gary Rosenthal told the newspaper.

'There were (none) that I know of that would indicate there were any problems, and the family seemed to be well liked, and the mother was very personable.

'It's one of those dilemmas you shake your head at.'