College friends Dias Kadyrbayev and Azamat Tazhayakov are accused of disposing of evidence from Tsarnaev's dormitory room. The 19-year-olds from Kazakhstan could be sent to prison for up to 20 years if found guilty of the conspiracy charges.
Authorities allege the pair tried to impede investigators' efforts by throwing away fireworks and other materials they found in Tsarnaev's room the day before he was captured following the April 15 blasts near the marathon finish line.
Police found the fireworks in a New Bedford landfill.
The defendants' attorneys maintain the pair, who like Tsarnaev were students at the University of Massachusetts, Dartmouth, did nothing wrong, WVCB-TV, Boston, reported.
Authorities later discovered the fireworks in a New Bedford landfill.
Tsarnaev, who is awaiting trial, and his older brother Tamerlan, who died in an encounter with police following, allegedly set off two bombs that killed three people and wounded scores of others. The two have been described as radicalized Muslims angered by the U.S. wars in Iraq and Afghanistan.