Michelle Carter
'You're finally going to be happy in heaven,' Michelle Carter (shown here at 17) told her boyfriend, Conrad Roy, shortly before he killed himself. Facebook

A Massachusetts teenager who urged her boyfriend to go through with his plans to kill himself must now stand trial for his death, a state court has ruled. Michelle Carter, 17 years old at the time of the 2014 suicide of her boyfriend Conrad Roy III, repeatedly encouraged him to follow through with his suicide plans.

"You need to stop thinking about this and just do it," she texted him in one of a number of messages just days before Roy's death from carbon monoxide poisoning at the age of 18.

"You're finally going to be happy in heaven. No more pain," she told him in one message. "It's okay to be scared and it's normal. I mean, you're about to die."

When the frightened boy finally locked himself in his car with the motor running, he reached out to Carter and the two talked on the phone for 47 minutes.

"He was scared," said prosecutor MaryClare Flynn. "She told him to get back in the car."

Carter's attorney argued to dismiss the charge of involuntary manslaughter against his client, saying that her actions didn't cause her boyfriend to commit suicide, and that Roy, who was being treated for a mental health issue, had tried to commit suicide on a previous occasion.

But the Supreme Judicial Court in Massachusetts ruled that a grand jury had probable cause to indict Carter on the involuntary manslaughter charge. The court ruled that Carter engaged in a "systematic campaign of coercion" and that her command to "get back in" the car during his final moments was a "direct causal link to his death."

Carter, now 19, has been out on bail and barred from social media since 2015. She is expected to enter a plea on 21 July. Her attorney, Joseph Cataldo, said he's confident his client will not be found guilty. He called her texts protected free speech. Cataldo labelled the case "a tragedy," but said "it is not a crime."

Roy's grandmother Janice Roy told Associated Press that the family is happy that Carter can be tried. Conrad was "very vulnerable at that stage," she said.