A court in the US has handed down a 15-month jail term against a young woman who encouraged her 18-year-old boyfriend to commit suicide in a series of text messages.

Michelle Carter was 17 when Conrad Roy died from carbon monoxide poisoning in Massachusetts in 2014.

The judge rejected claims that Carter was not responsible because of her lack of maturity or because of psychiatric medication she was taking, saying she had been “mindful” of her actions.

Conrad Roy III aunt wants Michelle Carter to get 20 years in prison for her role in Roy’s suicide. https://t.co/t4Ql5pNYUppic.twitter.com/pj20wo6Jbm — Boston Herald (@bostonherald) August 2, 2017

The accused had opted for a non-jury trial on a charge of involuntary manslaughter.

The jail term handed down was two and a half years, but 15 months of that was suspended. The judge agreed Carter could remain free during any appeals process.

Prosecutors had asked for a sentence of seven to 12 years.

Before the sentence was handed down, Assistant District Attorney Maryclare Flynn told the court: “Your Honor read thousands of text messages and knows how the defendant undertook a deliberate, well-thought-out campaign to cause the death of Conrad Henry Roy, quite simply for her own personal gain and quest for attention.

“To this date, the defendant has not accepted responsibility for Conrad’s death.

“She has blamed it on his fragile mental state, his family situation, her right to free speech or the medication that she was taking. She has shown no remorse.”

Roy’s father, also named Conrad Roy, had this to say to the court before the sentence was handed down: “Michelle Carter exploited my son’s weaknesses and used him as a pawn in her own well being.

“She has not shown any remorse. The fact that my son was convinced to kill himself makes his death unimaginable.

“How could Michelle Carter behave so viciously and encourage my son to end his life? Where was her humanity?”

The court heard about messages even sent as Roy sat in his parked truck in Fairhaven, Massachusetts, as it filled with carbon monoxide from a generator hooked up to it.

Roy got out of the truck as he became overwhelmed by the fumes but Carter urged him to “get back in.”

The court heard Roy had previously attempted suicide.

Carter’s defence attorney, Joseph Cataldo, told the judge before the sentencing: “Miss Carter does not, I suggest to this court, pose a danger to the public.

“I suggest that this sad, tragic manslaughter that she has now been convicted of was a very unusual set of circumstances unique to these two individuals: Conrad Roy and Michelle Carter, who were both struggling with mental health issues themselves.”