BOSTON (AP) — Lawyers for a woman who encouraged her boyfriend through text messages to take his own life have appealed her involuntary manslaughter conviction to the U.S. Supreme Court.

Michelle Carter's attorneys told the high court in a petition filed Monday that her conviction, based on her "words alone," violated her First Amendment right to free speech.

Carter began serving a 15-month jail sentence in February after Massachusetts' highest court upheld her 2017 conviction in Conrad Roy III's death.

One of her lawyers said in an emailed statement that Carter "did not cause Carter Roy's tragic death and should not be held criminally responsible for his suicide."

A judge found Carter caused Roy's death when she instructed him over the phone to get back in his truck as it was filling with toxic gas.

Two years after Carter was convicted of involuntary manslaughter in a case that gripped the nation, the director of a new documentary wants viewers to decide for themselves whether her actions were criminal.

The two-part film, debuting July 9 on HBO, digs into the legal case against Carter and explores a different side to the young Massachusetts woman portrayed by prosecutors as a cruel manipulator who coaxed Conrad Roy III into killing himself for attention.