Image copyright Unknown Image caption The Richard Family before the bombing. Martin, 8, seen un-obscured, died in the attack

The parents of youngest victim in the Boston marathon bombing have called on federal authorities to drop the death penalty as a possible punishment for bomber Dzhokhar Tsarnaev.

Bill and Denise Richard's eight-year-old son was one of three people killed in the explosions in April 2013.

The Richards said an execution sentence "could bring years of appeals and prolong reliving the most painful day of our lives."

Tsarnaev was convicted last week.

The Richards made their plea in a front-page piece in the Boston Globe on Friday.

"We are in favour of and would support the Department of Justice in taking the death penalty off the table in exchange for the defendant spending the rest of his life in prison without any possibility of release and waiving all of his rights to appeal," they wrote.

The Richards were injured in the attack and their daughter, Jane, lost one of her legs in one of the explosions.

"The defendant murdered our 8-year-old son, maimed our 7-year-old daughter, and stole part of our soul. 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," they said.

Image copyright Reuters Image caption The Richard family alongside Boston Mayor Marty Walsh at a ceremony marking two years since the attack

Throughout the piece, the Richards never mention Tsarnaev by name, electing instead to refer to him as "the defendant".

"I care deeply about their views and the views of the other victims and survivors," US Attorney for Boston, Carmen Ortiz, said. She refused to go into specifics.

Families of other victims have expressed support for the death penalty.

The court will begin the penalty phase of the trial on Tuesday, one day after this year's Boston Marathon.