Three college friends of Boston Marathon bombing suspect Dzhokhar Tsarnaev have been arrested and accused of removing a backpack containing hollowed-out fireworks from his dorm room three days after the attack to stop him getting into trouble.
In court papers, the FBI said one of them threw the backpack away - it was later found in a landfill by law enforcement officers -after the young men concluded from news reports that Tsarnaev was one of the bombers.
Azamat Tazhayakov and Dias Kadyrbayev, both 19-year-olds from Kazakhstan, were charged with conspiring to obstruct justice by concealing and destroying evidence.
Robel Phillipos, also19, who graduated from the prestigious Cambridge Rindge and Latin High School with Tsarnaev, was charged with lying to investigators about the visit to Tsarnaev's room.
The three were not accused of any involvement in the bombing itself. But in a footnote in the court papers outlining the charges, the FBI said that about a month before the bombing, Tsarnaev told Tazhayakov and Kadyrbayev that he knew how to make a bomb.
Lawyers for the Kazakh students said their clients had nothing to do with the bombing and were just as shocked by the crime as everyone else. Phillipos' lawyer, Derege Demissie, said outside court: "The only allegation is he made a misrepresentation."
At a court appearance this afternoon, the Kazakh students did not request bail and will face another hearing on May 14. Phillipos was held for a hearing on Monday.
Three people were killed and more than 260 injured when two bombs exploded near the finish line of the Boston Marathon on April 15. Tamerlan Tsarnaev died after a gunfight with police days later. His younger brother, Dzhokhar Tsarnaev, a 19-year-old student at the University of Massachusetts in Dartmouth, was captured and lies in a prison hospital.
Investigators have not said whether the pressure cooker bombs used in the attacks were made with gunpowder extracted from fireworks. Tazhayakov and Kadyrbayev have been held in jail for more than a week on allegations that they violated their student visas by not regularly going to class at UMassachusetts.
All three men charged on Wednesday began attending UMass with Tsarnaev in 2011, according to the FBI. If convicted, Kadyrbayev and Tazhayakov could get up to five years in prison and a 250,000 US dollar (£160,700) fine. Phillipos faces a maximum of eight years behind bars and a 250,000 dollar (£160,700) fine.