Boston marathon bomb suspect challenges death penalty

This, after last month's botched execution of a US inmate in Oklahoma

Lawyers for Boston Marathon bombing suspect Dzhokhar Tsarnaev have asked a US court to rule out capital punishment for their client, after last month's botched execution of a US inmate.

In documents filed late on Wednesday, Tsarnaev's legal team asked the judge to take the death penalty off the table in the federal capital murder case against Tsarnaev, accused in twin bombings that killed three people and injured 264 in April of last year.

"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.