A fourth person, a police officer, was killed by the suspects during the pursuit by authorities.
“The defense… requests that the court strike the death penalty as a possible punishment,” the lawyers wrote.
Their petition invoked “mounting evidence that innocent people have actually been executed in recent years in the United States.”
The defense lawyers also cited “public and worldwide revulsion over the recurring spectacle of botched executions” – including one in Oklahoma on April 29 that left a convicted killer writhing in agony after the state administered an untested lethal injection protocol.
Tsarnaev’s attorneys in their court filing also cited the “nearly total (and increasing) isolation of the United States as an executing nation among the democratic countries of the world.”
Dzhokhar Tsarnaev and his older brother Tamerlan allegedly carried out the attack near the finish line of the Boston Marathon, using pressure-cooker bombs hidden in their backpacks.
Tamerlan Tsarnaev, 26, was shot by police days after the bombings during an extensive manhunt.
Dzhokhar, 20, was wounded but taken alive and now is awaiting trial on 30 federal charges.
The trial has been set for November.
Defense attorneys have indicated that they might seek a change of venue, out of fears that Tsarnaev will not be able to receive a fair trial in the highly emotional case.
Federal death penalty cases are relatively rare in the United States, and are often reserved for the most heinous and notorious crimes.
Of the dozens of death sentences carried out since 1988, only three have been in federal cases.
The last of these, against Oklahoma City bomber Timothy McVeigh, was carried out in 2001, following the deadly 1995 bombing of a federal office building.
That bombing left 168 people dead and more than 600 injured.