AFP – Getty Images, file A federal magistrate has agreed to delay a probable cause hearing for Boston Marathon bombing suspect Dzhokhar Tsarnaev.

The judge overseeing the government's prosecution of Dzhokhar Tsarnaev, the surviving defendant in the Boston Marathon bombing case, has agreed to delay the next step in the case for roughly a month.

A probable cause hearing had been scheduled for May 30, but federal prosecutors and lawyers for Tsarnaev asked Magistrate Judge Marianne Bowler to delay it until July 2, citing what they called "the complex factual and legal issues present in this case and the need for adequate time to obtain and review evidence."

Such hearings are intended to determine whether the government has a strong enough case to continue legal proceedings. In practice, they seldom happen, either because the defendant waives the right to the hearing or because a grand jury issues an indictment before the hearing and the case moves on to arraignment and trial.

Under normal circumstances, the government must issue an indictment within 30 days of arrest, which would have been May 19 in Tsarnaev's case, but no indictment been issued. The U.S. attorney's office in Boston would not cite a specific reason, but a spokesman noted that federal rules permit a delay for several reasons, including the need to determine a defendant's physical condition.

After his capture, Tsarnaev, 19, spent six days in the hospital being treated for gunshot wounds before being transferred to a federal medical prison. He's charged with using a weapon of mass destruction for the April 15 blast that killed three and wounded more than 200 people at the finish line of the race.