good evening, everyone. i m erin burnett. breaking news, new details on what motivated the boston bombing suspects. i want to get to jake tapper live in boston. what have you you learned? reporter: according to a u.s. government official, talking to me, the investigators have been working very hard trying to get information from dzhokhar tsarnaev. what he has been able to tell them in these preliminary investigations indicates that, according to him, according to him, all of this information needs to be checked out and followed up by investigators, but according to him, the brothers were not in contact with any foreign terrorist group. they did this on their own. there was a big on-line component to how they were self radicalized. they watched videos on-line. they downloaded information on-line. they did not have e-mail communication, but they were very much self radicalized, self starters on-line. in addition, dzhokhar is saying the older brother, tamerlan, was the driving