Attorneys for convicted Boston Marathon bomber Dzhokhar Tsarnaev are trying to overturn his death sentence by arguing the 2013 terror attack was so nationally traumatic that it was impossible to get an impartial jury, according to court documents filed this week. Tsarnaev was convicted of carrying out the April 15, 2013, bombing with his older brother, who was killed by police. Lawyers who are appealing the death sentence argue his rights to a fair trial were violated because the jury was familiar with the broad details of the attack. Prosecutors maintain the jury was completely impartial.