Lawyers for Boston Marathon bombing suspect Dzhokhar Tsarnaev argued Wednesday that statements he made to authorities after he was arrested should be thrown out because, while suffering from gunshot wounds, he was questioned for 36 hours in a hospital room without being told his rights.

The lawyers said in a flurry of pretrial court filings that federal agents began questioning Tsarnaev about 20 hours after he arrived at the hospital in critical condition and that his statements cannot be considered voluntary.

Tsarnaev, 20, has pleaded not guilty to several federal charges. Prosecutors allege he and his brother, 26, planted two pressure cooker bombs near the marathon's finish line, killing three people and injuring more than 260. Tsarnaev was shot and his brother, Tamerlan Tsarnaev, was killed during a gunbattle with police on April 19, 2013, four days after the bombing. His lawyers said he had gunshot wounds to his head, face, throat, jaw, left hand and legs.

Federal investigators questioned Tsarnaev days after last year's bombing without formally telling him of his right to a lawyer under a public safety exception allowed when there's concern about an ongoing threat. But defense attorneys said the questioning continued "despite the fact that he quickly allayed concerns about any continuing threat to public safety, repeatedly asked for a lawyer, and begged to rest." They said his medical treatment included painkillers that impaired his judgment and increased his susceptibility to pressure.

The lawyers for Tsarnaev said his rights also were violated when his appearance in court was delayed to complete the interrogation, during which he told authorities about how the bombs were built and about the brothers' activities before and after the bombing.

"Agents made clear by word and deed that they would not allow him to see a lawyer until they had finished questioning him," his defense team's filing said.

Also on Wednesday, the defense asked the judge to declare the federal death penalty unconstitutional, citing recent bungled executions and arguing there's mounting evidence innocent people have been executed.

Tsarnaev's lawyers said the U.S. Constitution's protection against cruel and unusual punishment prohibits the application of the death penalty because it's not authorized under Massachusetts law. They cited "worldwide revulsion over the recurring spectacle of botched executions," including one that left an Ohio inmate snorting and gasping during the 26 minutes it took him to die in January and another that left an Oklahoma inmate straining to lift his head off a pillow after supposedly being rendered unconscious last month.

The lawyers also asked the judge to bar federal prosecutors from arguing that targeting a crowded event — the race drew 23,336 runners and an estimated 500,000 spectators — is a factor a jury should consider when weighing his possible punishment if he's convicted.

The lawyers said the decision to bomb the marathon shouldn't be an "aggravating factor" in determining whether he should receive the death penalty because prosecutors also argue he committed the offense after substantial planning to cause death and commit an act of terrorism.

"Stated differently, the allegation that Tsarnaev targeted the marathon is simply a more specific statement of the substantial planning allegation," Tsarnaev's lawyers wrote in a court filing.

Federal law requires the jury to reach its sentencing decision by weighing each aggravating factor cited by prosecutors against mitigating factors cited by the defense. Tsarnaev's lawyers said having duplicative aggravating factors "can have no other effect than to introduce arbitrariness and unfairness into the jury's sentencing deliberations."

Federal prosecutors are expected to respond in their own filings.

Last week, the defense asked a judge to eliminate another aggravating factor cited by prosecutors: Tsarnaev's alleged betrayal of the United States. Tsarnaev's lawyers said prosecutors, by citing his status as a newly naturalized U.S. citizen, are implying he's "more deserving of the death penalty" than a native-born person who commits the same crime.

Tsarnaev's lawyers acknowledge that a federal appeals court rejected a challenge to the federal death penalty in another Massachusetts case in 2007. But they asked the judge to eliminate the death penalty as a possible punishment if they can show prosecutors gave erroneous instructions to the grand jury that indicted him.

The Associated Press