He also downloaded extremist Muslim literature, including "Defense of the Muslim Lands, the First Obligation After Imam," which advocates "violence designed to terrorize the perceived enemies of Islam," the indictment said.
Another tract downloaded included a foreword by Anwar al-Awlaki, an American propagandist for al-Qaida who was killed in a U.S. drone strike, federal prosecutors said.
U.S. Attorney Carmen Ortiz of Massachusetts said it will be up to Attorney General Eric Holder to decide whether to pursue the death penalty against Tsarnaev.
The indictment assembled and confirmed details of the case that have been widely reported over the past two months, and added new pieces of information.
For example, it confirmed that Tamerlan Tsarnaev bought 48 fireworks mortar shells containing about eight pounds of explosive powder from a Seabrook, N.H., fireworks store. It also disclosed that he used the Internet to order electronic components that could be used in making bombs.
The papers detail how the brothers then placed knapsacks containing shrapnel-packed bombs near the finish line of the 26.2-mile race.
The court papers also confirm that Dzhokhar Tsarnaev contributed to his brother's death by accidentally running him over with a stolen vehicle during a shootout and police chase.
The charges cover the slaying of Massachusetts Institute of Technology police officer Sean Collier, who authorities said was shot in the head at close range in his cruiser by the Tsarnaevs during their getaway attempt. The brothers tried to take his gun, prosecutors said.
In addition, prosecutors said that during the carjacking, the Tsarnaev brothers forced the motorist to turn over his ATM card and his password, and Dzhokhar Tsarnaev withdrew $800 from the man's account.
At the same time the federal indictment was announced, Massachusetts authorities brought a 15-count state indictment against Dzhokhar Tsarnaev over the MIT officer's slaying and the police shootout.