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.