Carter had waived her right to a jury trial, meaning that members of the community did not render the verdict; Moniz acted exclusively as jury.
In part of Judge Moniz's reasoning, the judge said Carter, in addition to her texts, had urged the boy during a phone call to get back in the truck that was being filled with deadly poison and that she did not alert authorities that Roy was taking his life. Carter was also on the phone with Roy for almost an hour while he was killing himself, and she urged him to get back in the vehicle when he hesitated.
Prosecutors argued meanwhile that, when Roy got out of his truck, Carter told him to "get back in". And finally, she did not issue a simple additional instruction: "'Get out of the truck.'" the judge said.
Conrad revealed that Carter's family has not reached out before or after the verdict. She is also not allowed to leave the state.
The judge set sentencing for August 3.
The sensational trial in Taunton offered a window into teen depression and suicide through text messages and Facebook communications.
Conrad had driven alone to a Kmart parking lot and hooked up a water pump that emitted carbon monoxide into the cab of his truck.
"When are you doing it?" she asked repeatedly in text messages. Carter wrote in one message.
Carter's attorney argued she was a troubled, delusional young woman who was "dragged" into the suicidal journey of Roy, who was long intent on killing himself. He pointed out that Roy had stepped out of the truck, and told Carter he couldn't go through with it.
The judge said he did not take into account in his verdict Roy's previous suicide attempts. That at any time she could have contacted his family and tell them how he was feeling or even say where he could be found.
Conrad Roy, Jr, father of Conrad Roy III, comforts his daughter Camdyn Roy in court.
He said Carter, then 17, had a duty to call someone for help when she knew Roy was attempting suicide. You're just making it harder on yourself by pushing it off. "You can't keep living this way".
"I am not going to sleep until you are in the auto with the generator on", she wrote in one text. Carter and Roy met in Florida in 2012 while both were on vacation with their families. Their relationship largely consisted of text messages and emails.
"This court, having reviewed the evidence and applied the law there to now find you guilty on the indictment charging you with the involuntary manslaughter of the person Conrad Roy the third".
According to AP, Carter cried as the judge explained his reasoning but was "stoic" as he read the verdict.
Carter, 20, broke down crying in court, putting her head in her hands, before Judge Lawrence Moniz announced the verdict.
Conray Roy, 18, of Mattapoisett, Mass., who killed himself on July 12, 2014, with coaching from his girlfriend Michelle Carter.