(USA TODAY) -- A Massachusetts federal grand jury returned a 30-count indictment against Boston bombing suspect Dzhokhar Tsarnaev on Thursday, charging the 19-year-old Cambridge man in the deaths of three bombing victims and the separate slaying of a Boston-area campus police officer.
The officer was fatally shot three days after the April 15 assault on the Boston Marathon.
Tsarnaev, also facing charges of using a weapon of mass destruction and the use of a firearm resulting in death among other criminal counts, faces a possible death sentence on 17 of the charges if convicted.
Officials declined to comment on whether a decision has been reached to seek the death penalty, but Attorney General Eric Holder said the indictment "proves our unyielding resolve to hold accountable, to the fullest extent of the law, anyone who would threaten the American people or attempt to terrorize our great cities.''
"The (government) is firmly committed to achieving justice on behalf of all who were affected by these senseless acts of violence,'' Holder said.
Tsarnaev's lawyers did not immediately respond to a request for comment.
In addition to the federal indictment, Middlesex County, Mass., District Attorney Marian Ryan said a local grand jury had issued a separate indictment charging Tsarnaev with 15 criminal counts, which also included the murder of Massachusetts Institute of Technology police officer Sean Collier.
The federal indictment alleges that for three months beginning in February, Tsarnaev conspired with his brother, Tamerlan Tsarnaev, to use improvised explosives -constructed with pressure cookers, black powder, nails and ball bearings - in an attack on the Boston Marathon. According to the indictment, the brothers detonated the bombs seconds apart near the crowded finish line of the race, killing three and injuring more than 250 others.
At an undisclosed time before the assaults, according to the indictment, Dzhokhar Tsarnaev downloaded to his computer at least four radical treatises, one containing an essay by slain al-Qaeda leader Anwar al-Awlaki, which "directs Muslims not to give their allegiance to governments that invade Muslim lands.''
Three days after the bombings, shortly after the Tsarnaevs' photographs were made public by the FBI, the brothers allegedly drove to the MIT campus armed with five explosive devices, a semi-automatic handgun, a machete and hunting knife. There they shot and killed Collier and attempted to steal his service weapon. The murder triggered a new crime spree in which the brothers allegedly carjacked a local man's Mercedes at gunpoint and forced him to turn over a bank card, which they used to siphon $800 from the hostage's account before he escaped uninjured.
Tamerlan Tsarnaev was killed in a violent encounter with police hours later. During that confrontation, in which the brothers allegedly heaved four of the explosive devices and fired on the officers, a fleeing Dzhokhar Tsarnaev drove over his fallen brother, "seriously injuring him and contributing to his death.''
Dzhokhar Tsarnaev was captured April 19, hiding in a dry-docked boat parked in the driveway of Watertown, Mass., home.
Following his removal from the boat, according to the court documents released Thursday, authorities found a series of messages scrawled on the inside wall and beams of the boat.
"The U.S. government is killing our innocent civilians ... I can't stand to see such evil go unpunished ... We Muslims are one body, you hurt one you hurt us all ... Now I don't like killing innocent people it is forbidden in Islam but due to said (unintelligible word) it is allowed ... Stop killing our innocent people and we will stop.''
"The defendant's conduct forever changed lives,'' Boston U.S. Attorney Carmen Ortiz said during a briefing announcing the charges. "The victims, their families and this community have shown extraordinary strength and resilience in the face of this senseless violence.''
Tsarnaev is scheduled to be arraigned on the charges July 10.