A lawyer for Plainville teenager Michelle Carter asked the state’s highest court Thursday to halt the prosecution against her for allegedly encouraging a friend to kill himself, asserting that she did not commit a crime by urging Conrad Roy III to return to his truck and let toxic fumes overcome him.
Carter’s conduct may have been reprehensible, defense attorney Dana Alan Curhan acknowledged during questioning by the Supreme Judicial Court. Yet her insistence that Roy take his own life — at one point allegedly texting him “It’s now or never” — did not make her responsible for the 18-year-old’s death from carbon monoxide poisoning in July 2014, he said.
Roy took his own life, and Carter was not with him at the time of his suicide, Curhan said. They mostly communicated by text and phone before he died.
“Telling him to do it was not the cause,” Curhan said.
The digital communications between Roy and Carter, who was 17 at the time, are at the center of an involuntary manslaughter case that has grabbed national attention with its wrenching depiction of the teens’ discussion over Roy’s desire to end his life.
In exchanges detailed in court records, Carter assures him that she’ll be there for his family when he is gone. In their final messages before Roy’s death, Carter implores him, “You just have to do it like you said.”
The case has also examined the legal boundaries of speech that motivates individuals to harm themselves. On Thursday, judges repeatedly asked lawyers for both sides about the line between encouragement and criminal manslaughter.
Noting that Massachusetts is one of only 11 states without a law against encouraging someone to commit suicide, Curhan said the state is facing a high bar in the case. Carter did not threaten or coerce Roy into harming himself, he said.
Carter might have been more culpable, he said, “if she was physically present, and she said, ‘Get back in the truck, or I’ll put you back in there myself.’ ”
The prosecution of Carter is on hold as the SJC reviews a juvenile court judge’s decision to let the case go to trial. Carter has pleaded not guilty, and her lawyers have pressed for the case to be thrown out.
Relatives of Roy, who lived in Mattapoisett, say they hope the high court’s decision will recognize that electronic communication is a powerful form of emotional connection for teenagers, and that his exchanges with Carter — through messages and calls — had a powerful effect on him.
Becki Maki, Roy’s aunt, said the teenager’s father was in court for the first time Thursday, as the SJC held oral arguments.
“It’s difficult to hear,” Maki said. “We’ve seen what everybody else has seen, and it’s undeniable to us that she did have something to do with his decision.”
Shoshana Stern, an assistant district attorney in Bristol County, told the court that Carter was “way over the line” of criminality when she encouraged him to get back in his truck when he had second thoughts. Stern said that some of Carter’s urgings could be read as threats, bolstering the prosecution’s case against her.
“I think she made it clear in her conversations with him from prior discussions that she would be deeply disappointed in him if he didn’t carry through, she would be angry with him, and she also said ‘If you don’t do this, I’m going to get you help,’ ” Stern said.
In the context of their relationship, it was clear that Roy “feared that deeply,” she said, and did not think “hospitals would help.”
Stephen J. Weymouth, a veteran Boston defense lawyer who is not involved in the case, said he understands the prosecution’s point of view, but said they face a uphill climb, despite the case’s emotional resonance.
“There’s got to be more than merely a couple of thoughtless, heartless statements in order to charge someone with something as serious as involuntary manslaughter,” he said.
The charges against Carter have drawn a vivid picture of the events leading to Roy’s death. Authorities have said that Carter “had a full understanding” of his suicide plan, and was in close contact with him in the hours before his death, even as she expressed concerns about his safety to her friends.
“I’m losing all hope that he’s even alive,” Carter wrote a friend, according to court records. She then texted Roy, “Let me know when you’re gonna do it.”
While some of Roy’s relatives are closely following the court proceedings, his grandfather, Dave Bozzi, is not. Bozzi said he hopes Carter will face consequences, but worries his grandson will not receive justice.
“If you love somebody, you try to discourage them from doing something like that. You don’t encourage them,” he said. “They can throw all the psychobabble at it that they want. I don’t care.”
Martin Finucane of the Globe staff contributed to this report. Andy Rosen can be reached at email@example.com.