Phillipos faces a maximum of eight years behind bars and a $250,000 fine if convicted.
Tsarnaev and his 26-year-old brother, Tamerlan, are accused of carrying out the April 15 bombing, which used pressure cookers packed with explosives, nails, ball bearings and metal shards. The attack killed three people and injured more than 260 others near the marathon’s finish line.
Tamerlan Tsarnaev died after a gunfight with police days later. Dzhokhar Tsarnaev, 19, was captured and remains in a prison hospital. He has been charged with using a weapon of mass destruction and faces a potential death sentence if convicted.