The surviving Boston bombing suspect is awake and responding to questions in writing, several US media outlets reported late Sunday.
Dzokhar Tsarnaev, who is being treated in hospital for serious wounds sustained during a manhunt, is the main suspect behind Monday's twin bombings that killed three people and wounded 180 others at the Boston Marathon. His older brother, killed in a shootout with police, is also a suspect.
NBC News, citing federal officials, reported that despite a throat injury that keeps him from talking, the 19-year-old was beginning to respond to questions from investigators.
ABC News said Tsarnaev was responding "sporadically" in writing and that investigators were asking about other potential cell members and unexploded bombs.
USA Today also cited a law enforcement official as saying he was awake and responding in writing, adding that investigators were probing the possibility that his neck wound was self-inflicted.
Earlier Sunday, Boston Police Department Commissioner Ed Davis had told reporters that Tsarnaev was in "critical but stable condition."