Dzhokhar Tsarnaev, suspected co-author of the Boston Marathon bombings, on Wednesday pleaded not guilty to the 30 charges leveled against him in connection with the deadly April 15 attack.

Tsarnaev was arraigned before U.S. District Judge Marianne Bowler in a Boston courtroom where attack victims and two of the 19-year-old defendant's sisters were present.

Tsarnaev stands accused of 30 charges, including causing the deaths of three people in the bomb blasts and that of an MIT campus police officer three days later while he was fleeing authorities and using a weapon of mass destruction.

He appeared calm in an orange prison jumpsuit with his left arm in a cast and long and unruly hair, and his face seemed somewhat swollen, perhaps due to the injuries he suffered in a shootout with police several days after the attack.

Smiling at times, Tsarnaev said only "not guilty" multiple times when the judge asked him how he wanted to plead with regard to the charges, 17 of which could carry the death penalty.

About 150 people, including reporters, filled the public benches in the courtroom, where about 30 attack victims and relatives of the approximately 280 people killed or wounded in the attack were also present.

Among those attending the hearing were people who demonstrated outside the court in favor of Tsarnaev and who consider him the victim of a U.S. government conspiracy.

Tsarnaev is scheduled to appear before the judge again on Sept. 23.

At the close of the hearing, Tsarnaev was taken the courtroom and was returned to the prison hospital in Massachusetts where he is being held surrounded by heavy security.

After allegedly planting, along with his older brother Tamerlan, two homemade bombs near the finish line of the Boston Marathon, Dzhokhar was captured four days later after a spectacular flight and pursuit lasting almost 24 hours and during which his brother died after a shootout with police. EFE