Michelle Carter was convicted in the 2014 death of her boyfriend, Conrad Roy. She was 17 at the time.
Carter had asked the Supreme Court to vacate the conviction on the grounds that her right to free speech under the First Amendment protected her from being responsible for Roy's suicide.
The court declined to review the case, without comment from any individual justice, which allows the conviction to stand.
Roy, who was 18, poisoned himself with carbon monoxide in a Kmart parking lot in Fairhaven, Massachusetts, after exchanging text messages and speaking twice on the phone with Carter on that summer day. She lived about 50 miles away.
Carter's conviction was upheld last February by the Massachusetts Supreme Judicial Court, which "rejected the defendant's claim that her words to the victim, without any physical act on her part and even without her physical presence at the scene, could not constitute wanton or reckless conduct sufficient to support a charge of manslaughter."
In her petition to the court, Carter called the conviction "unprecedented," and pointed to states that have invalidated findings of culpability in cases of assisted suicide and cyberstalking. Carter's lawyers said her right to free speech shields her from criminal responsibility because her involvement was limited to "words alone."
In response, Massachusetts Attorney General Maura Healey in court filings noted the scores of text messages, in which Carter and Roy discussed the method he'd chosen to kill himself.
Carter "knew Roy had previously attempted suicide but had abandoned or foiled his own attempts, and she taunted him that he would purposely fail in killing himself again."
Carter "carried out a 'systematic campaign of coercion' that 'targeted the equivocating young victim's insecurities and acted to subvert his willpower in favor of her own' in the last weeks of his life," Healey wrote.
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