Authorities say three college friends of the surviving Boston Marathon bomber didn't want him to get in trouble for it.

They say the three students concluded from news reports three days after the bombings that Dzhokhar Tsarnaev was one of the bombers. According to court papers, they went to Tsarnaev's dorm room and found a backpack with fireworks that had been emptied of powder.

The FBI says the three removed the backpack and a laptop from the room, and went to an apartment to watch news reports featuring photographs of Tsarnaev.

According to the affidavit, one of the men told authorities that the three then decided together to "throw the backpack and fireworks into the trash because they did not want Tsarnaev to get into trouble."

Two of the men, from Kzakhstan, have been held in jail for more than a week on allegations that they violated their student visas.

The three aren't accused of any direct involvement in the bombing. But according to court papers, the FBI said that about a month before the bombing, Tsarnaev told two of them that he knew how to make a bomb.