Videos of Conrad Roy now key evidence in texting suicide trial

The videos teenager Conrad Roy made before killing himself are now key evidence in the manslaughter trial of his friend, Michelle Carter. Roy's videos offer a glimpse of the 18-year-old's struggles with depression, where he speaks candidly about his inner turmoil.

"This is Conrad Henry Roy III reporting about social anxiety," Roy said in one video.

At times, Roy seemed brimming with hope in his videos, reports "48 Hours" correspondent Erin Moriarty.

"I just got a job from the Boston Duck Tours to captain their boat. Like that's a huge accomplishment," Roy said.

But later, his despair came into focus.

"This no good trash will never be successful. I'll have no life, never have kids, never learn," Roy said.

Prosecutors say Carter bombarded Roy with texts and urged him to take his life because she wanted attention.

Prosecutors introduced the videos before resting their case Thursday. But the videos could also help the defense. Carter's attorneys argue Roy was already suicidal long before he met her.

In July 2014, Roy died inside a truck from carbon monoxide poisoning. As he was dying, prosecutors say he was on the phone with Carter for 46 minutes. Days before, in numerous texts, Carter, then 17, offered Roy suggestions on how to take his own life and lectured him when he wavered.

"But I'm tired of you not taking this seriously, like if you aren't really gonna do it then stop pretending that you are," one message said.

Another read: "Hang yourself, jump off a building, stab yourself I don't know there's a lot of ways."

Carter's lawyers say investigators ignored texts she sent trying to help him.

"I'm trying to do the best to dig you out – you're not aware of that, are you?" the defense lawyer asked, referring to a text message sent by Carter.

"No, I'm not," Massachusetts state police Sgt. Michael Bates said.

"And you're probably not aware that he said, 'I don't want to be dug out?'" the lawyer asked.

"No," Bates said.

"Are you aware that he said he wanted to kill himself?"

"No," Bates said.

The defense is expected to blame Carter's medication for her odd behavior and argue responsibility for Roy's death ultimately lies with him.

"And the manner of death?" the defense asked.

"Yes, I marked that as a suicide," medical examiner Dr. Faryl Sandler said.

"And there was also a box you could have marked a homicide?" the lawyer asked.

"Correct," Sandler said.

In order to be convicted on the manslaughter charge, the judge would have to agree Carter's words caused Roy's death, even though she was 35 miles away. Massachusetts is one of only 11 states without a law making it a crime to encourage a suicide.