Boston Marathon bombing suspect Dzhokhar Tsarnaev has pleaded not guilty to 30 charges, including use of a weapon of mass destruction to kill.

He entered the pleas Wednesday in Federal Court in Boston.

For his first plea, the 19-year-old, the left side of his face swollen and his arm in a cast, leaned toward a microphone and said, "Not guilty." He then said not guilty repeatedly about a half-dozen more times.

He was led out of the courtroom in handcuffs.

Federal prosecutors are deciding whether to pursue the death penalty for the teen.

Authorities believe he and older brother Tamerlan planted two pressure-cooker bombs, which killed three people and wounded more than 260 near the finish line at the April 15 marathon. The older brother was killed three days later following a shootout with police. The younger Tsarnaev was later found hiding in a boat in a suburban backyard.

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A courtroom sketch depicts accused Boston Marathon bomber Dzhokhar Tsarnaev during his arraignment in federal court on Wednesday. The 19-year-old appeared to have a swollen cheek and his arm was in a cast. (Margaret Small/AP)

Tsarnaev was initially charged in the hospital, where he was recovering from wounds suffered during that shootout.

Prosecutors have also charged the surviving brother in the death of Sean A. Collier, a 27-year-old Massachusetts Institute of Technology police officer who was shot three days after the bombings.

In court, Tsarnaev smiled at his two sisters as he arrived shortly after 3:30 p.m. ET. One sister was carrying a baby, the other wiped away tears with a tissue.

Prosecutors say Tsarnaev wrote about his motivations for the attack on the inside walls and beams of the boat where he was captured. Among the writings was a line that said he "didn't like" killing innocent people. Another read: "We Muslims are one body, you hurt one you hurt us all."

Four hours before entering his pleas, the defendant arrived at the courthouse in a four-vehicle motorcade that included a van, a Humvee and a state police car.

About a dozen supporters cheered at his approach yelling, "justice for Jahar," as Tsarnaev is known. One woman held a sign that read, "Free Jahar."

Three people — Martin Richard, 8, Krystle Marie Campbell, 29, and Lingzi Lu, 23 — were killed in the bomb blasts. Authorities believe the Tsarnaevs also killed Massachusetts Institute of Technology officer Sean Collier days after the marathon bombing while they were on the run.

Numerous bombing victims had legs amputated after the two explosions, which detonated along the final stretch of the race a few hours after the elite runners had finished.

The proceedings took place in a heavily guarded courtroom packed not only with victims but with their families, police officers, members of the public and the media.

Wednesday's arraignment marks Tsarnaev's first public appearance since he was arrested April 19.