Three college friends of Boston Marathon bombing suspect Dzhokhar Tsarnaev have been charged by police investigating the attacks.
Azamat Tazhayakov and Dias Kadyrbayev are charged with conspiring to obstruct justice. A third man, Robel Phillipos, is charged with making false statements to federal investigators.
The suspects are accused of removing a backpack containing fireworks emptied of gunpowder from Tsarnaev's dorm room three days after the bombings.
In court papers, the FBI said Tazhayakov and Kadyrbayev agreed to throw the backpack in the garbage after concluding from news reports that Dzhokhar Tsarnaev was one of the bombers.
Law enforcement officers later found the backpack in a landfill.
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Tazhayakov and Kadyrbayev, who came to the US from Kazakhstan, have been held in jail for more than a week on allegations they violated their student visas while attending college.
There is also information that Tazhayakov was allowed to re-enter the US in January from Kazakhstan despite not having a valid student visa.
The Kazakhs waived bail during an initial court appearance on Wednesday. They are scheduled to appear in court again on May 14.
Phillipos, a US citizen, is being held pending a detention and probable cause hearing scheduled for Monday.
Attorneys for Kadyrbayev and Tazhayakov told reporters on Wednesday their clients did not know the items they removed from Tsarnaev's room were linked to the attacks.
Tazhayakov's attorney, Harlan Protass, said: "My client feels horrible and was shocked to hear that someone he knew was involved in the bombings."
Kadyrbayev's lawyer, Robert Stahl, said his client "absolutely denies the charges".
Both men face a maximum sentence of five years in prison and a \$250,000 fine, the US Justice Department said.
Phillipos faces up to eight years in prison and a \$250,000 fine.
All three men, aged 19, began attending the University of Massachusetts at Dartmouth with Tsarnaev at the same time in 2011, according to the FBI.
The university said in a statement that Tazhayakov has been suspended "pending the outcome of the case". The school said Phillipos and Kadyrbayev are not currently enrolled.
The trio were not accused of any involvement in the bombing itself. But in a footnote in the court papers, the FBI said that about a month before the bombing, Tsarnaev told Tazhayakov and Kadyrbayev that he knew how to make a bomb.
Three people were killed and more than 260 injured on April 15 when two bombs exploded near the finish line.
Suspect Tamerlan Tsarnaev died after a gunfight with police several days later. His brother Dzhokhar was captured and lies in a hospital prison.
The surviving brother, 19, faces federal charges of using a weapon of mass destruction and malicious destruction of property resulting in death over the double bombing.
Authorities say the brothers also killed an MIT police officer as they tried to escape, although no charges have been filed yet over his death.
The White House and investigators have previously suggested that the Tsarnaevs could have acted alone, without ties to any foreign government or terrorist organisation.
But law enforcement authorities have kept a close watch on some of the brothers' contacts as they try to establish whether they had any help.