BOSTON — The two brothers suspected of bombing the Boston Marathon appear to have been motivated by a radical brand of Islam but do not seem connected to any Muslim terrorist groups, U.S. officials said Monday after interrogating and charging Dzhokhar Tsarnaev with crimes that could bring the death penalty.

Tsarnaev, 19, was charged in his hospital room, where he was in serious condition with a gunshot wound to the throat and other injuries suffered during his attempted getaway. His older brother, Tamerlan, 26, died Friday after a fierce gunbattle with police.

The Massachusetts college student was charged with using and conspiring to use a weapon of mass destruction. He was accused of joining with his brother in setting off the shrapnel-packed pressure-cooker bombs that killed three people and wounded more than 200 a week ago.

The brothers, ethnic Chechens from Russia who had been living in the U.S. for about a decade, practiced Islam.

Two U.S. officials said preliminary evidence from the younger man's interrogation suggests the brothers were motivated by religious extremism but were apparently not involved with Islamic terrorist organizations....