Dzhokhar Tsarnaev is seen in this photograph released by the FBI on April 19, 2013.

Boston - A friend of the accused Boston Marathon bomber charged with interfering with the investigation into the blasts said on Monday he had no idea he could have walked away from hours of questioning four days after the attack.

Lawyers for the friend, Kazakh exchange student Dias Kadyrbayev, are trying to persuade a federal judge to throw out statements he made under interrogation in a police station, after being ordered out of his apartment by heavily armed agents, saying his comments were not voluntary.

Kadyrbayev, 20, is one of three college friends of accused bomber Dzhokhar Tsarnaev charged with hampering the investigation by going to the suspect's dormitory room at the University of Massachusetts at Dartmouth three days after the attack and removing a laptop and backpack containing empty fireworks shells.

Kadyrbayev and fellow Kazakh exchange student Azamat Tazhayakov were questioned for hours the night of April 19, 2013, although neither was arrested until the following day. During hearings last month, officials said the pair would have been free to leave the police station where they had been brought in handcuffs had they asked.

“The way they were interrogating me, it wasn't like, 'Sure, you can go anytime’,” Kadyrbayev told a US District Court hearing in Boston. “I just felt I ain't free.”

Kadyrbayev's lawyers argue his statements should not be admitted at his upcoming trial because he had no attorney present and did not understand the consequences of speaking with agents. One agent testified Kadyrbayev told him he suspected Tsarnaev had been involved in the attack.

Tazhayakov's attorneys dropped a similar request to challenge his early statements to law enforcement, saying they did not want their client to testify at a pretrial hearing.

Three people were killed and 264 injured in the April 15, 2013, bombing at the historic Boston Marathon.

Kadyrbayev's understanding of English was too rudimentary for him to have understood paperwork informing him he had a right to remain silent, said Temple University linguist Aneta Pavlenko.

“It was highly unlikely that at the time of interrogation, Mr Kadyrbayev had the linguistic proficiency to understand the Miranda warning,” Pavlenko testified.

An interpreter translated for Kadyrbayev, whose first language is Russian, throughout Monday's hearing. Prosecutors said it was the first time he had asked for translation after almost a year of court proceedings.

Assistant US Attorney Stephanie Siegmann asked Kadyrbayev if he recalled attending a day-long deposition in July 2013.

“There was a translator in the room... You never asked him to translate any words for him, did you?” Siegmann asked.

“No,” Kadyrbayev replied.

Kadyrbayev and Tazhayakov, both charged with obstruction of justice, could face up to 25 years in prison if convicted. A third friend, Robel Phillipos of Cambridge, Massachusetts, faces up to 16 years if convicted of the less serious charge of lying to investigators.

Tsarnaev, who also is accused of killing a university police officer in a shootout three days after the bombings, is awaiting trial in a prison west of Boston. He faces the possibility of execution if convicted. - Reuters