BOSTON — The Massachusetts Supreme Court ruled Friday a teenager who authorities say sent text messages encouraging a friend to kill himself must stand trial on a criminal charge of involuntary manslaughter.

The decision means Michelle Carter will be prosecuted for the death by suicide of Conrad Roy III, then 18, two years ago from carbon monoxide poisoning in his pickup truck.

Carter, 17 at the time of Roy’s death, was indicted a year ago by a grand jury under the state’s youthful offender law. She could face 20 years in prison if convicted.

The case has attracted national attention because lawyers say it ties to the legal limits of free speech in the digital age, especially when it motivates harm but does not threaten it.

The Supreme Court found Carter’s conduct in the case was sufficient to require her to stand trial “because a conviction of involuntary manslaughter is punishable by imprisonment in state prison and inherently involves the infliction of serious bodily harm.”

Carter’s defense attorneys  argued at an April court hearing her text statements encouraging Ray to take his life did not make her responsible for his death; that the final decision was his own, as was the method. They also noted she was not present when he took his life.

Prosecutors released text messages at the hearing between Carter and Roy on the night of his death in support of the involuntary manslaughter charge.  The texts implored Roy to go through with his suicide plan.

“You just need to do it,” Carter said in a text. “You can’t keep living this way.”

When Roy replied, “I do want to but I’m freaking for my family I guess. I don’t know,” Carter responded: “Conrad, I told you I’ll take care of them. Everyone will take care of them to make sure they won’t be alone and people will help them get through it. We talked about this and they will be okay and accept it. People who commit suicide don’t think this much. They just do it.”

She later texted: “You just have to do it like you said.”

Prosecutors said Carter and Roy had also talked to each other for 47 minutes on their cell phones prior to his death. Those conversations were not publicly disclosed.

Roy was described by friends at the time as a popular teen who suffered from anxiety. He lived in Mattapoisett on the south coast of Massachusetts. His family had requested prosecution of Carter.