In July 2014, Michelle Carter's 18-year-old boyfriend committed suicide in a K-Mart parking lot.

After his death, Carter texted a friend.

"Like, honestly I could have stopped it," she wrote.

But instead of trying to stop her teenage boyfriend from taking his life, prosecutors in Massachusetts believe that Carter pressured Conrad Roy to go through with the act.

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And on Saturday, the state's highest court ruled that she could go to trial for her alleged role in his death.

"I hope they hold her accountable for her actions," Roy's grandfather, Conrad Roy snr, told the Boston Globe.

"She told him to get back in the truck. She prodded him on. All of the text messages are pretty much self-explanatory."

The Supreme Judicial Court's ruling - which found that a grand jury was justified in returning an indictment in Carter's case - was unanimous, the Associated Press reported.

Carter, who was 17 at the time of Roy's death, faces a charge of involuntary manslaughter.

Prosecutors have alleged that Carter pressured Roy to go through with suicide, counselled him on his fears and researched suicide methods.

Text messages between the two propelled the case into a national spotlight and highlighted Carter's alleged role.