>> 8:25, does michelle carter now send you another text that you receive later on that night? . >> and what does she tell you? >> i think he just killed himself. >> reporter: she testifies about that incriminating text from michelle. >> i was on the phone with him and he got out of the car because it was working and he got scared. and i [ bleep ] told him to get back in. >> reporter: isn't that pretty incriminating stuff? >> yeah. >> yes. and she goes on to say, i could have called police. i could have called his family. but she didn't. what she did do with him, three minutes, is start texting the guy she was trying to date and her other friend, sam boardman, and talking to them about, oh, it's all about me, what am i going to do now? >> she essentially put him back into a gas chamber, she listened to him gasp for air, take his last breath, and die, and she did nothing. >> reporter: michelle's defense resting nearly entirely on one witness, psychiatrist peter breggin. how could the girl who's most likely to brighten your day encourage her boyfriend to take his life? >> the shor