The brothers are ethnic Chechens from Russia who had been living in the U.S. for about a decade.
The next step in the legal process against Tsarnaev is likely to be an indictment, to which federal prosecutors could add new charges. State prosecutors have said they expect to charge Tsarnaev separately in the killing of the MIT officer.
Federal public defender Miriam Conrad, whose office has been asked to represent Tsarnaev, asked that two death penalty lawyers be appointed to represent Tsarnaev, "given the magnitude of this case."
A probable cause hearing — at which prosecutors will spell out the basics of their case — was set for May 30. According to a clerk's notes of Monday's proceedings in the hospital, U.S. Magistrate Judge Marianne Bowler indicated she was satisfied that Tsarnaev was "alert and able to respond to the charges."
Tsarnaev did not speak during the proceeding, except to answer "no" when he was asked if he could afford his own lawyer. He nodded when asked if he was able to answer some questions and whether he understood his rights.
Conrad declined to comment when contacted by The Associated Press.
The criminal complaint outlining the allegations shed no light on the motive for the attack.
In the criminal complaint, investigators said Dzhokhar Tsarnaev and his brother each placed a knapsack containing a bomb in the crowd near the finish line of the 26.2-mile race. The FBI said surveillance-camera footage showed Dzhokhar manipulating his cellphone and lifting it to his ear just moments before the two blasts.
After the first blast, a block away from Dzhokhar, "virtually every head turns to the east ... and stares in that direction in apparent bewilderment and alarm," the complaint says. But Dzhokhar Tsarnaev, unlike practically everyone else around him, appeared calm, the FBI said.