The family of the Massachusetts Institute of Technology police officer who was killed by Boston Marathon bomber Dzhokhar Tsarnaev and his brother, Tamerlan, has filed a lawsuit against the convicted terrorist's friend.

In the suit, which was filed on Wednesday, relatives of MIT Officer Sean Collier alleged that Tsarnaev's close friend and former college classmate, Dias Kadyrbayev, could have taken steps that would have prevented Collier's death.

Collier was fatally shot by Tsarnaev and his now deceased older brother just hours after the pair detonated two pressure cooker bombs at the Boston Marathon on April 15, 2013.

However, Collier's relatives claim Kadyrbayev had "the ability to change the course of history" and prevent the MIT police officer's death, reports the Boston Herald. Instead, the suit claims that Kadyrbayev chose to protect a terrorist by removing evidence from the bomber's dorm room following the attack.

Along with the lawsuit, Collier's stepfather Joseph Rogers submitted a five-page victim impact statement, saying: "In that moment, there was no one to protect him because no one spoke up, no one cared enough about his life to do the right thing."

Rogers also stated: "Had the defendant done the right thing, and called the police, the Tsarnaev brothers' murderous rampage across Cambridge and Watertown may have been prevented."

Rogers added that the loss of Collier "on our family is immeasurable." His murder "could absolutely have been prevented."

Federal prosecutors are seeking a seven-year sentence for Kadyrbayev, a Kazakhstan national.

Last year, Kadyrbayev pleaded guilty to impeding the bombing investigation. He is scheduled to be sentenced on June 2, reports The Associated Press.

In May, a jury sentenced Tsarnaev to death after he 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.