Three friends of one of the Boston Marathon bombing suspects, Dzhokhar Tsarnaev, have been arrested. Two of those friends are Russian-speaking immigrants from Kazakhstan who are accused of trying to cover up Tsarnaev's involvement in the bombing. The F.B.I. says the men put a backpack and fireworks into a black trash bag and then tossed the trash bag into a dumpster. They are being charged with destroying evidence. The third friend, an American citizen, is being charged with lying to investigators. None are being charged with direct involvement in the April 15th bombings. Phillip Martin is a senior investigative reporter for our partner WGBH, and he's been looking into the criminal complaints against the three.