Carter cried and clutched a handkerchief to her face as Moniz detailed her conduct and the circumstances of Roys death, but she was stoic when the verdict was formally pronounced.
Prosecutors said Carter also told Mr Roy to "get back in" when he got out of his truck.
Carter did that despite knowing "all of the feelings" Roy had shared with her previously, including a prior attempt to drown himself, Mr Moniz said.
Roy's father, Conrad Roy Jr., said, "This has been a very tough time for our family". "Finally, she did not issue a simple additional instruction [to Roy]: 'Get out of the truck'".
WATCH: Carter sobbed as the verdict was handed down. Her sentencing hearing was scheduled for August 3.
Carter is charged in the suicide of her 18-year-old boyfriend, Conrad Roy III.
A MA woman was convicted of involuntary manslaughter after a judge Friday ruled a barrage of text messages led to her boyfriend's suicide. "The time is right and you're ready, you just need to do it!" to him, and at one point, when the teen got scared and exited his vehicle, Carter told him to "get back in" the auto.
Carter's lawyer Joseph Cataldo had argued that Roy was already suicidal before meeting Carter and that Roy was exclusively responsible for his own actions.
The verdict, handed down by a judge in a non-jury trial, was a rare legal finding that, essentially, a person's words alone can directly cause someone else's suicide.
Carter's attorney argued she was a troubled, delusional young woman who was "dragged" into the suicidal journey of Roy, who has always been intent on killing himself.
Moniz said in court on Friday that he did not buy Breggin's testimony. The New York Times reports that Carter had first attempted (via her texts) to talk Roy out of killing himself when he initially expressed a desire.
What do you think of Michelle Carter's conviction? You're just making it harder on yourself by pushing it off.
"If you point a gun at somebody, you're pretty much intending to shoot them", Gutterman said. In another exchange, Carter told Roy she would look like a "fool" if he didn't kill himself perhaps because she'd been telling people her boyfriend was suicidal. Roy and Carter had been in contact with each while he died. Their relationship largely consisted of text messages and emails.
Michelle Carter, now 20, was convicted in Bristol Juvenile Court in a case that could have broad implications for how prosecutors and judges address criminal intent in the age of instant communication and ubiquitous social media engagement.