Lawyers for Boston Marathon bombing suspect Dzhokhar Tsarnaev  have asked a judge to bar prosecutors from arguing that his alleged decision to target the iconic athletic event is one of the factors a jury should consider when weighing whether he should be sentenced to death.

In a court filing Wednesday, Tsarnaev's lawyers argued that listing the decision to bomb the marathon as an ``aggravating factor'' is duplicative because prosecutors also allege that Tsarnaev committed the offense after substantial planning to cause death and commit an act of terrorism.

His lawyers also filed a separate motion asking the judge to declare the federal death penalty unconstitutional.

Tsarnaev awaits trial in the April 15, 2013, bombing. Prosecutors allege he and his brother planted two bombs near the finish line, killing three people and injuring more than 260.