New York - A 20-year-old woman went on trial in the US state of Massachusetts on Tuesday, accused of persuading her teenage boyfriend to kill himself, in a case that could break new legal ground.Michelle Carter is charged with involuntary manslaughter and has waived her right to a jury trial, meaning her fate will be decided by a judge. She faces up to 20 years in prison if convicted.Conrad Roy, 18, was found dead from carbon monoxide poisoning in his pickup truck in a parking lot in July 2014.The prosecution contends that Carter and Roy exchanged hundreds of text messages in which Carter urged him to follow through on his plan to kill himself."By her wanton and reckless conduct, she committed a felony," assistant district attorney Maryclare Flynn told the court in Taunton, south of Boston. "She put him in the car that night. She listened to him as he died.""When are you going to do it? Stop ignoring the question," added the prosecutor, reading from one of Carter's alleged text messages. "Just do it babe," the defendant allegedly wrote in another.The prosecution says Carter helped Roy devise the plan to use carbon monoxide poisoning, encouraged him to conceal it from his parents, lie to his mother and select a secluded parking lot.'Needy person' The defendant was a "very needy person" with few friends who used Roy as a "pawn" to get attention from girls at high school, the prosecutor argued."She has to be the grieving girlfriend to get the sympathy and the attention that she believes she deserves," Flynn said.While legal experts say Carter may have encouraged him to take his own life, they have questioned whether it is enough to secure a conviction under involuntary manslaughter.The northeastern state of Massachusetts, unlike other US states, has no law against encouraging someone to commit suicide. "This is a suicide case," defence lawyer Joseph Cataldo told the court. "It is not a homicide."Roy had been on a path to suicide "for years", he said. Carter urged him to seek professional help and suffered from her own mental health frailties, he added.The defence also sought to minimise 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.Carter is being tried in a juvenile court. In the months after Roy's death, she reportedly raised hundreds of dollars for mental health awareness.