A college friend of Boston Marathon bomber Dzhokhar Tsarnaev has been sentenced to six years in prison for impeding the investigation into the 2013 attacks.

Dias Kadyrbayev apologized to the bombing victims and their families at his sentencing hearing Tuesday, saying he is ashamed he didn't call police when he recognized photos of Tsarnaev as a suspect.

Kadyrbayev pleaded guilty last year to obstruction of justice and conspiracy charges for removing items from Tsarnaev's dorm room after recognizing his friend in photos released by the FBI days after the bombing.

He had faced up to seven years in prison.

Kadyrbayev told the judge Tuesday: "I really can't believe that I acted so stupidly."

Three people were killed and more than 260 were injured in the bombing.