Federal prosecutors Thursday announced they will seek the death penalty against 20-year-old Dzhokhar Tsarnaev in the Boston Marathon bombing, accusing him of betraying his adopted country by ruthlessly carrying out a terrorist attack calculated to cause maximum carnage.

U.S. Attorney General Eric Holder's decision to press for Tsarnaev's execution was widely expected. The twin blasts last April killed three people and wounded more than 260, and over half the 30 federal charges against Tsarnaev — including using a weapon of mass destruction to kill — carry a possible death sentence.

"The nature of the conduct at issue and the resultant harm compel this decision," Holder said in a statement of just two terse and dispassionate sentences that instantly raised the stakes in one of the most wrenching criminal cases Boston has ever seen.

Tsarnaev has pleaded not guilty. No trial date has been set....