A federal grand jury Thursday charged two friends of Boston Marathon bombing suspect Dzhokhar Tsarnaev with obstructing justice and conspiracy to obstruct justice, the U.S. attorney's office in Boston said.

Azamat Tazhayakov and Dias Kadyrbayev -- 19-year-old roommates and Kazakh nationals who began attending the University of Massachusetts-Dartmouth the same semester as Tsarnaev -- were charged in May with conspiracy.

It is not clear whether Thursday's indictment represents a second conspiracy charge.

Thursday's indictment accuses Tazhayakov and Kadyrbayev of helping Tsarnaev after the April 15 bombing by taking items from his dorm room to keep them from investigators.

If convicted, Tazhayakov and Kadyrbayev could be sentenced to a maximum 20 years in prison on the obstruction count and up to five years on the conspiracy count, the U.S. attorney's office said. They also could be fined $250,000.

Arkady Bukh, Tazhayakov's attorney, said his client is not discouraged. He also said that Tazhayakov did not touch any of Tsarnaev's items.

"He feels very strongly he'll be able to be able to convince a jury that's he's innocent," Bukh said. "There's no evidence of intent, no incentive to help (Dzhokhar), no motive to destroy anything."

The three students socialized and texted each other, the indictment says.

On April 18, three days before the FBI searched Tsarnaev's dorm room, Tazhayakov and Kadyrbayev allegedly went into the dorm, took Tsarnaev's laptop and a backpack containing Vaseline, a thumb drive, fireworks and a "homework assignment sheet" and took them back to their New Bedford apartment, the indictment states.

"The fireworks container has been opened and manipulated," the indictment says. "As a result, some of the explosive powder was visible."

Kadyrbayev told his roommate that he believed Tsarnaev "used the Vaseline 'to make bombs,' or words to that effect," the indictment states.

That day, Kadyrbayev showed Tazhayakov a text message from Tsarnaev that read, "If yu want yu can go to my room and take what's there (smiley face emoticon) but ight bro Salam aleikum."

Either that night or early the next day, Kadyrbayev tossed the backpack in a Dumpster, according to the charges.

"Over the course of two days," the indictment continues, "more than 30 federal agents searched (a New Bedford) landfill for the evidence Kadyrbayev had placed in the trash."

The indictment further says the roommates watched April 18 news reports about the bombing that featured photos of Tsarnaev.

A federal grand jury earlier this year returned a 30-count indictment against Tsarnaev, the surviving suspect in the bombings, that alleges he used a weapon of mass destruction.

Tsarnaev is charged with killing four people -- three spectators who died in the bombings and a Massachusetts Institute of Technology police officer ambushed in his cruiser a few days later -- and "maiming, burning and wounding scores of others," U.S. Attorney Carmen Ortiz said.