Officials briefed on the interrogation say the 19-year-old suspect went silent after a magistrate judge and a representative from the U.S. Attorney's office gave him his Miranda warning. The officials insisted on anonymity because the briefing was private.
Before being advised of his rights, Tsarnaev told authorities that his 26-year-old brother, Tamerlan, recently had recruited him to be part of the attack that detonated pressure-cooker bombs at the marathon finish line, say two U.S. officials.
The exact timeline is unclear. A transcript of the court proceeding shows Bowler asking a doctor if Tsarnaev was "alert."