BOSTON — Attorneys for Boston Marathon bomber Dzhokhar Tsarnaev asked a judge Tuesday to hold a new trial for their client, citing a Supreme Court decision that a U.S. law stiffening sentences for crimes committed while in possession of a gun was overly broad.

Tsarnaev was sentenced on June 24 to death by lethal injection in the 2013 bomb attack, which killed three people and injured more than 260.

Defense lawyers on Tuesday argued that Tsarnaev’s conviction and sentence were tainted by the law, which affected half of the 30 criminal counts he faced.

The high court found the law overly broad in a hearing on an unrelated case two days after Tsarnaev was sentenced.

“It’s really impossible to unpack what weight that (ruling) might have had on the jury’s deliberations, in their weighing of aggravating and mitigating factors,” defense attorney William Fick said. “It requires a redo of the entire sentencing proceeding.”

Federal prosecutors questioned the relevance of the argument, given the magnitude of the attack. Tsarnaev’s attorneys admitted on the first day of the trial that he played a role in the bombing, and the 22-year-old apologized before sentencing.

“There is absolutely no reason to believe … the result would have been any different” had the charges had no reference that Tsarnaev and his older brother were in possession of a handgun during the attack, said Assistant U.S. Attorney William Weinreb.

U.S. District Judge George O’Toole did not immediately rule on the request.

Tsarnaev is being held at the Supermax high-security prison in Florence, Colorado, while his attorneys appeal his death sentence. He was not present in court Tuesday.

He was last seen in public on June 24, when he said he was “sorry for the lives I have taken.”

His older brother, Tamerlan, who participated in the April 15, 2013 attack, died after a gunbattle with police three days after the bombing.

Martin Richard, 8; Chinese exchange student Lingzi Lu, 26; and restaurant manager Krystle Campbell, 29, died in the bombing. Three days later, the Tsarnaevs shot dead Massachusetts Institute of Technology police Officer Sean Collier, 26.

The legal wrangling over Tsarnaev’s fate could play out for years, if not decades. Just three of the 74 people sentenced to death in the United States for federal crimes since 1998 have been executed.