New York (AFP)

A 20-year-old US woman was convicted of involuntary manslaughter Friday for ordering her teenage boyfriend to follow through on his long-planned suicide and for failing to save him from harm.

Michelle Carter broke down in tears and sobbed into a tissue during the 20-minute juvenile court hearing in Massachusetts, which is likely to break new ground in a state that has no law against encouraging someone to commit suicide.

Conrad Roy, 18, was found dead from carbon monoxide poisoning in his pickup truck in a parking lot in July 2014.

The trial heard that Carter and Roy exchanged hundreds of text messages in which the young woman, who was 17 at the time, urged him to follow through on his plan to kill himself, to conceal it from his parents and lie to his mother.

But Judge Lawrence Moniz said it was her instruction to Roy to get back into the vehicle -- during a telephone call after he stepped out -- and her failure to sound the alarm that was crucial to the conviction.

Failure to take reasonable steps to alleviate the risk to another "can result in a charge of manslaughter," he noted in his decision.

"This court, having reviewed the evidence and applied the law thereto, now finds you guilty on the indictment charging you with the involuntary manslaughter of the person Conrad Roy," Moniz told the packed court room.

Carter, who waived her right to a jury trial, faces up to 20 years in prison. She will remain on bail until sentencing on August 3 in Taunton, south of Boston.

In the closely-watched case, legal experts had questioned whether Carter's actions were enough to secure a conviction under involuntary manslaughter.

The defense argued that Roy had been on a path to suicide "for years" and sought to minimize Carter's role in her boyfriend's life, saying the pair were in a "long-term texting relationship" and had met in person only a handful of times.

The judge agreed that Roy had been "struggling" and "took significant action" himself, such as extensive research, securing a generator, water pump, parking his vehicle in an unnoticeable area and starting the pump.

- 'No action' -

"However he breaks that chain of self-causation by exiting the vehicle, he takes himself out of the toxic environment," Moniz said.

He did the same thing during previous attempts on his life, pausing to tell someone -- first a parent and then a friend who got him help.

But it was different when he told Carter, in July 2014.

"Instructing Mr Roy to get back into the truck constitutes wanton and reckless conduct by Miss Carter, creating a situation where there is a high degree of likelihood that substantial harm would result to Mr Roy," the judge said.

In subsequent text messages to friends, Carter admitted to hearing him coughing and the loud noise of the motor, the judge noted.

Prosecutors told the trial that the defendant stayed on the telephone listening to her boyfriend as he died in the truck.

"She called no one," Moniz said, despite knowing where he was and having his family's telephone numbers. "And finally, she did not issue a simple additional instruction: 'get out of the truck'."

The judge rejected a theory of involuntary intoxication raised by psychiatrist Peter Breggin, a defense witness who testified that Carter's own medication would have hindered her state of mind.

Conrad Roy's father, who has the same name as his son, welcomed the verdict, and thanked the judge before bursting into sobs.

"This has been a very tough time for our family," he told reporters.

"In reality there are no winners here today," prosecuting attorney Katie Rayburn said.

"Two families have been torn apart and will be affected by this for years to come. With that being said, we fervently hope that today's guilty verdict will bring some measure of justice to the friends and family of Conrad Roy."

Agence France-Presse

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