Flowers are laid on the Boston Marathon finish line Getty

The parents of the youngest victim of the 2013 Boston marathon bombing have called on US federal authorities to drop the death penalty as a possible punishment for convicted bomber Dzhokhar Tsarnaev.

Bill and Denise Richard's eight-year-old son, Martin, was one of three people killed in the terror attack on 15 April 2013, when two pressure cooker bombs exploded near the finish line of the race.

In a front-page piece published in the Boston Globe on 17 April, they said an execution sentence "could bring years of appeals," forcing the family to relive "the most painful day of our lives."

"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 eight-year-old son, maimed our seven-year-old daughter, and stole part of our soul," they said.

Tsarnev brothers
Dzohkar Tsarnaev (left) and his brother Tamerlan carried out the Boston Marathon bombings FBI

"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."

Choosing not to refer to Tsarnaev by name, the Richards expressed their wish to begin to rebuild their lives after his sentencing.

"As long as the defendant is in the spotlight, we have no choice but to live a story told on his terms, not ours," they said.

"The minute the defendant fades from our newspapers and TV screens is the minute we begin the process of rebuilding our lives and our family."

Tsarnaev was convicted last week. The sentencing phase of his trial will begin the day after this year's Boston Marathon on 21 April.