After asking a carjacking victim, “Did you hear about the Boston Marathon explosion?,” one of the accused bombers took credit for the terror act, saying, “I did that,” according to criminal charges unsealed today.

In a federal criminal complaint, Dzhokhar Tsarnaev, 19, is charged with using a weapon of mass destruction in connection with the April 15 attack.

The complaint was unsealed this afternoon following a proceeding in Tsarnaev’s room at Beth Israel Deaconess Medical Center, where he is in serious but stable condition. A federal magistrate advised Tsarnaev of his rights and the charges filed against him by Department of Justice prosecutors. Tsarnaev, who was represented by William Fick, a federal public defender, is scheduled for a May 30 probable cause hearing.    

The U.S. District Court document reveals that when Tsarnaev (seen above) and his brother Tamerlan allegedly carjacked a vehicle last Thursday evening, one of them “removed the magazine from his gun and showed the victim that it had a bullet in it, and then re-inserted the magazine.” One of the brothers then stated, “I am serious.”

The carjacking victim was able to escape when the carjackers exited the vehicle at a “gas station/convenience store” in Cambridge. Tamerlan Tsarnaev was killed late Thursday during a shootout with law enforcement officers.

The charge against Tsarnaev, according to an affidavit sworn by FBI Agent Daniel Genck, is supported by surveillance video and photos showing him “apparently slipping his knapsack onto the ground,” where “an explosion occurs in the location where Bomber Two had placed his knapsack.”

The complaint also reveals that an FBI search of Tsarnaev’s dormitory recovered “a large pyrotechnic,” BBs, and a black jacket and white hat similar to those “worn by Bomber Two at the Boston Marathon.”

Agent Genck also reports that when Tsarnaev was apprehended Friday evening, his “visible injuries” included “apparent gunshot wounds to the head, neck, legs, and hand.”