The parents of Martin Richard, an 8-year-old boy who was killed in the Boston Marathon bombing, are pleading with federal prosecutors to spare the life of their son's killer.

In an open letter published in the Boston Globe Friday, William and Denise Richard urged prosecutors not to sentence the convicted terrorist, 21-year-old Dzhokhar Tsarnaev, to death, which could potentially prolong the process and anguish for victims and their families.

"We understand all too well the heinousness and brutality of the crimes committed. We were there. We lived it. The defendant murdered our 8-year-old son, maimed our 7-year-old daughter, and stole part of our soul," reads the letter.

They went on to call on the U.S. government to intervene and stop prosecutors from seeking the death penalty, which could lead to years of appeals.

"We know that the government has its reasons for seeking the death penalty, but the continued pursuit of that punishment could bring years of appeals and prolong reliving the most painful day of our lives. We hope our two remaining children do not have to grow up with the lingering, painful reminder of what the defendant took from them, which years of appeals would undoubtedly bring," states the letter.

Earlier this month, Tsarnaev was found guilty of 30 charges for his role in the 2013 Boston Marathon bombings, including conspiracy to use a weapon of mass destruction and bombing a public place. The charges also covered a carjacking that took place in the aftermath of the attack, the deadly shooting of a Massachusetts Institute of Technology police officer, and a gunfight in Watertown, Massachusetts, in which Tsarnaev and his deceased brother tossed explosives at police.

During the trial, defense lawyers argued that Tsarnaev participated in the attack that killed Richard and two others on April 15, 2013, because he was under the influence of his older brother, Tamerlan, who then died during a shootout with police three days later.

In the second phase of Tsarnaev's trial, which is scheduled to begin Tuesday, it will be up to the same jury to decide whether Tsarneav should face life in prison or death, reports The Washington Post.