Boston Marathon bombing: US seeks seven-year jail term for Tsarnaev's friend Dias Kadyrbayev

US federal prosecutors are seeking seven years in prison for a friend of convicted Boston Marathon bomber Dzhokhar Tsarnaev who pleaded guilty to obstruction of justice in August.

Dias Kadyrbayev, of Kazakhstan, is one of three friends of Tsarnaev who are scheduled to be sentenced for interfering in the investigation of the bombing that killed three and injured over 260.

According to Reuters, Kadyrbayev was in the United States as an exchange student when he and two friends visited Tsarnaev's dorm room after the FBI released photos of Tsarnaev and his brother Tamerlan.

Kadyrbayev, fellow Kazakh Azamat Tazhayakov and Cambridge local Robel Phillipos reportedly recognised Tsarnaev as one of the suspects of the bombing but did not call law enforcement authorities. Kadyrbayev and Tazhayakov also removed a backpack containing empty fireworks shells from the bomber's dorm room three days after the April attacks.

That night, the Tsarnaev brothers shot and killed MIT police officer Sean Collier. The ensuing shootout with police resulted in Tamerlan's death.

"There is no evidence that Kadyrbayev was aware of Tsarnaev's plan to bomb the Boston Marathon or played any role in that terrorist attack," the prosecutors said. "Nevertheless, Kadyrbayev conspired with Tazhayakov to obstruct a terrorism investigation."

Kadyrbayev also allegedly admitted to recognising Tsarnaev's involvement on a Russian social media site, Reuters reported. "My best friend did this," he wrote in a post used by the prosecution. "They hijacked a car, killed a policeman."

According to Reuters, Collier's step-father Joseph Rogers also filed a statement with the court on 27 May. "The defendant had the tools and the ability to change the course of history," he said. "He chose to say nothing, and because of that, he has taken everything away from us. He has taken our son."

Due to his guilty plea, Kadyrbayev will be spared a 25-year prison sentence. He is scheduled to be sentenced on 2 June. Tazhayakov, found guilty of obstruction of justice, and Phillipos, found guilty of lying to investigators, are scheduled to be sentenced on 5 June.