A friend of Boston Marathon bomber Dzhokhar Tsarnaev (joh-HAHR' tsahr-NEYE'-ehv) has dropped an appeal of his conviction for obstructing the investigation into the bombing.

In court documents filed by his lawyer Thursday, Azamat Tazhayakov (AZ'-maht tuh-ZAY'-uh-kahv) says he "knowingly and voluntarily" elects to withdraw his appeal.

Tazhayakov was sentenced last month to 3 1/2 years in prison after he tearfully apologized to Boston residents for impeding the investigation into the 2013 attack while authorities frantically searched for Tsarnaev and his brother.

He was convicted of conspiracy and obstruction of justice for agreeing with another friend to remove Tsarnaev's backpack from his University of Massachusetts Dartmouth dorm room. The bag contained fireworks that had been emptied of their explosive powder.

Tsarnaev was sentenced to death.