(CNN) -- Unable to speak, the surviving suspect in the Boston Marathon bombings has been communicating with authorities in writing, a senior federal official briefed on the investigation told CNN Monday.

Investigators have been questioning Dzhokhar Tsarnaev since Sunday, according to a second source -- a senior law enforcement official.

Neither source would say what, if anything, Tsarnaev has been telling investigators about his alleged role in the bombing that killed three and wounded more than 170 a week ago Monday.

http://www.cnn.com/2013/04/22/us/boston-attack/index.html?hpt=hp_t1