BOSTON — It was three days after the stunning bombing of the Boston Marathon, and the FBI was asking for the public's help in identifying two suspects by releasing photos of them mingling with the crowd.

Hours later, three friends of Dzhokhar Tsarnaev were in his dorm room. One was later convicted of obstructing the bombing investigation by removing items from Tsarnaev's room while a second pleaded guilty to identical charges; a third was convicted of lying to the FBI.

All three — friends who attended the University of Massachusetts-Dartmouth with Tsarnaev — face sentencing this week.

Azamat Tazhayakov and Dias Kadyrbayev, both natives of Kazakhstan, impeded the investigation by taking Tsarnaev's backpack and computer from his dorm room. Robel Phillipos lied about being with them in Tsarnaev's room when they removed the items.

Three people were killed and more than 260 were injured in the April 15, 2013, bombing. Tsarnaev, 21, has been condemned to death by a federal jury and is awaiting formal sentencing on June 24.

Prosecutors say there is no evidence any of the friends knew of plans by Tsarnaev and his older brother to bomb the marathon, but they are asking for seven years in prison for Kadyrbayev and four years for Tazhayakov for impeding the investigation into the attack at a time when authorities were frantically searching for the bombers.

In sentencing memos filed in court, prosecutors say both men had the power to help law enforcement identify Tsarnaev and prevent additional violence, possibly including the murder of MIT police Officer Sean Collier, who was killed by the Tsarnaev brothers as they tried to flee the area after the FBI released their photos. Tamerlan Tsarnaev, 26, died after a shootout with police.

"Hours before (Dzhokhar) Tsarnaev murdered Officer Collier, the defendant (Kadyrbayev) recognized that his friend Tsarnaev was the fugitive bomber. Any reasonable, decent person possessed of the information the defendant had would have recognized that immediate apprehension of Tsarnaev was a public-safety imperative," prosecutors wrote in their sentencing memo for Kadyrbayev.

Kadyrbayev's lawyers are objecting to a bid by prosecutors to allow Collier's family to give victim impact statements during his sentencing hearing, arguing that he did not cause Collier's death.

"The Tsarnaev brothers alone are responsible for the murder of Sean Collier," attorneys Robert Stahl and Laura Gasiorowski wrote in a court filing.

Judge Douglas Woodlock granted a motion to seal the defense sentencing memo from public view so it is unclear what sentence Kadrybayev's lawyers are seeking. They did not return a call seeking comment.

Tazhayakov's attorney, Arkady Bukh, said he is hoping the judge will sentence Tazhayakov to time served for the two years he has already spent in custody.

Bukh said Tazhayakov has an enormous amount of sympathy for the victims of the bombings and "had absolutely no desire to shield nor support the terrorist." He said that when the FBI released the photos, Tazhayakov had a "level of uncertainty" on whether Tsarnaev was really one of the suspects. Bukh said even Tazhayakov has difficulty explaining why he did what he did.

"This is not a gentleman or a boy who is a jihadist and has clear intent to destroy America ... this is the guy who just made the wrong move at the wrong time," Bukh said Monday.

After Tazhayakov was convicted of conspiracy and obstruction of justice, Kadyrbayev pleaded guilty to the same charges under an agreement with prosecutors who will recommend that he serve no more than seven years in prison. Kadyrbayev is scheduled to be sentenced Tuesday.

Tazhayakov and Phillipos are scheduled to be sentenced Friday in separate hearings. Phillipos faces up to eight years in prison. His lawyers also did not immediately return calls seeking comment.