Transcript for Alleged Marathon Bomber Reveals Details of Attack

Good morning, america. A whole lot going on. You know, he is revealing so much more on how and why he carried out the marathon bombings with his brother. All the communication in writing, except for one word. When asked if he can afford a lawyer, he said no. And he's been formally charged with using a weapon of mass destruction and malicious destruction of property. And that also could face the death penalty. No question about it. Abc's brian ross is in boston with the exclusive, new details on the interrogation. Good morning, brian. Reporter: Good morning, george and robin. The 19-year-old suspect has admitted his role in the bombings. Speaking with a special team of fbi agents, who did not have to give him his legal rights. The suspect also revealed, according to authority, much of the how and the why of the deadly bomb blast. For all the fear and drama that the attacks produced -- the younger brother reportedly told agents, it was almost entirely done from the internet, homegrown, with no direction from overseas. They used an al qaeda internet description of how to make a pressure cooker bomb. They took a very simple recipe and targeted -- the boston marathon. Reporter: The decision to target the marathon came only in the last few weeks. According to the criminal complaint, he confessed to the bombing, telling the victim, i did that. As to inspiration, authorities tell abc news, dzhokhar said he and his brother were following the internet preachings of anwar al awlaki, the jihadist who has been dead for a year and a half. The older brother was particularly influenced by awlaki. Reporter: His brother was motivated for the attack. His brother believed in the wars in afghanistan and iraq, killing muslims. Reporter: Hours after the younger brother talked, authorities swarmed an area behind a cambridge drugstore, looking for more explosives or the place where the bombs might have been built. The fbi hopes to get additional insight from tamerlan's wife. A rhode island native, she converted to islam and changed her name from katherine to karina. Her family lawyer said monday, she was shocked to lrn of her husband's role and had no idea until the fbi first released those surveillance pictures of him and named him a suspect. The wife doesn't speak any russian and didn't really know what was going on. As to the younger brother's claims and statements to the fbi, investigators don't necessarily take as face value all he has said. He has every reason to try to minimize his own role as the investigation into possible ties to overseas groups in russia remains a central focus of the case, george. Brian, talk about living double-lives. The younger brother was out partying on wednesday night. Now, he's learned more about where the older brother, tamerlan, was, the day before the shoot-out. Reporter: Exactly. On that thursday, the day the fbi released his surveillance photo, he was at home taking care of his infant daughter, while his wife was at work.

This transcript has been automatically generated and may not be 100% accurate.