On April 15, a pair of bombs went off near the finish line of the Boston Marathon. Since then, the 19-year-old Tsarnaev has been charged with 30 federal counts. Each of the counts could give him a life-in-prison sentence, and 17 are eligible for the death penalty.
Three people died in the initial bombing, including an 8-year-old boy. Dozens more lost limbs. Days after the attack, he was charged with killing a Massachusetts Institute of Technology police officer.
His appearance at the arraignment Wednesday is the first time he has been seen publicly since he was taken into custody.
Prosecutors are expected to use between 80 and 100 witnesses in a trial that will take up to four months.