Tazhayakov is the first of three friends to go on trial on charges of obstructing the investigation. Lawyers gave their opening statements to a jury in federal court in Boston.
Like Tsarnaev, Tazhayakov, Dias Kadyrbayev and Robel Phillipos were students at the University of Massachusetts Dartmouth. The three allegedly removed items from Tsarnaev's dorm room.
Tsarnaev, 20, is awaiting trial and could receive a death sentence if he is convicted. He and his older brother, Tamerlan, allegedly set off two bombs at the marathon finish line on April 15, 2013, killing three people and injuring 260.
Assistant U.S. Attorney Stephanie Siegmann told jurors that Tazhayakov and the others knew of Tsarnaev's extremist views before the bombing and that he told them martyrs would "go straight to heaven." She also charged the three knew the brothers were suspects several hours before the FBI released their names.
Tazhayakov helped remove items from Tsarnaev's room on April 18, she said. Tamerlan Tsarnaev was killed in a confrontation with police the next day and his brother was arrested hours later.
Defense lawyer Nicholas Woolridge urged jurors to be impartial.
"I hope you give this kid a shot," he said.