The girlfriend of a friend of Boston Marathon bombing suspect Dzhokhar Tsarnaev is expected to testify against another friend during his trial on obstruction of justice charges, according to lawyers for the man.

In a court filing Monday, lawyers for Azamat Tazhayakov said Bayan Kumiskali provided evidence under an immunity agreement with the government.

Kumiskali is the girlfriend of Dias Kadyrbayev, who attended the University of Massachusetts-Dartmouth with Tsarnaev and Tazhayakov. The three men were friends.

Tazhayakov and Kadyrbayev, natives of Kazakhstan, are charged with removing items from Tsarnaev's dorm room several days after the April 2013 bombing. The attack killed three people and injured more than 260.

Prosecutors allege that Kadyrbayev and Tazhayakov went to Tsarnaev's dorm room three days after the bombings and removed Tsarnaev's backpack containing fireworks with explosive powder and his laptop computer. The items were removed the same night the FBI released photos of Tsarnaev and his older brother, Tamerlan, as suspects in the bombings.

An indictment alleges that Kadyrbayev put the backpack with the fireworks in a trash bin outside their New Bedford apartment after Tazhayakov agreed. The backpack was later recovered in a local landfill.

The men have pleaded not guilty. They are not accused of participating in the bombings or knowing about the attack beforehand.

Tazyahakov's trial is scheduled to begin June 30, while Kadyrbayev is slated to go on trial in September. A third friend, Robel Phillipos, charged with lying to investigators, faces a separate trial in late September.

Tazhayakov's lawyers have asked the judge at his trial to instruct the jury to use "particular caution" when evaluating Kumiskali's testimony, "given that she was given an agreement from the government not to be prosecuted for her role in the alleged conduct."

"They may have had reason to make up stories or exaggerate what others did because they want to help themselves," attorney Nicholas Wooldridge wrote in the filing, referring to witnesses who testify under immunity agreements.

Wooldridge would not comment when asked if Kumiskali is also expected to testify against Kadyrbayev and Phillipos. Attorney Arkady Bukh, who also represents Tazhayakov, said he expects Tazhayakov to testify at his trial.

"He's looking forward to come to the trial, to tell the truth," Bukh said. "He is saying the whole family had great respect for this country and the city of Boston, and they feel for the people injured during the explosion.

"He just wants to come out and tell the truth of his non-involvement in the situation."