(CNN) -- Boston bombing suspect Dzhokhar Tsarnaev, who has been hospitalized since his capture Friday, has been communicating with officials, two sources tell CNN. Once senior law enforcement source says: "They have been questioning him since yesterday. There is some form of communication between law enforcement and the suspect." A senior federal official briefed on the investigation said the communication has been in writing. Neither source would discuss what Tsarnaev has been communicating.