BOSTON — In the weeks after two bombs exploded near the finish line of the 2013 Boston Marathon, prosecutors charged three of the surviving suspect’s friends with obstructing the investigation or lying to authorities.

More than a year later, they charged a fourth friend for deleting computer files and lying about certain details of his relationship with a second suspect.

As the first friend heads to trial this week, some defense attorneys and others are criticizing the extent to which federal prosecutors have charged the men, who are not accused of participating in the attack or knowing about it in advance.

Azamat Tazhayakov is charged with conspiracy and obstruction of justice for allegedly agreeing with another college friend, Dias Kadyrbayev, to remove Dzhokhar Tsarnaev’s backpack from his dorm room after learning he was a suspect in the bombing, which killed three people and injured more than 260. Opening statements in his trial were scheduled for today in U.S. District Court.

Kadyrbayev, who faces a separate trial in September, is accused of throwing out the backpack, which contained fireworks that had been emptied of black powder, a bomb-making ingredient. A third college friend, Robel Phillipos, is accused of lying to authorities.

Defense lawyers have reserved their harshest criticism for the prosecution of the fourth man, Khairullozhon Matanov, a 23-year-old cab driver from Quincy who was charged in May.

Prosecutors say Matanov was a friend of Dzhokhar’s brother, Tamerlan, who died in a shootout with police. Matanov is accused of lying to the FBI, particularly about the contact he had with the Tsarnaevs after the bombings, including dinner at a restaurant the night of the attack and multiple phone calls that week.

Matanov is accused of deleting files on his computer after the FBI released the brothers’ photos publicly three days after the bombing. He went to police the next morning and gave authorities their names, address and cellphone numbers. By that time, Tamerlan Tsarnaev was dead, and Dzhokhar was the object of a massive manhunt. He was later captured in a Boston suburb.

Some say prosecutors are not only justified but also have an obligation to charge anyone they believe impedes a terrorism investigation.