Robert Crimo, the suspected gunman in the July 4 shooting in Highland Park, Illinois, pleaded not guilty to more than 100 charges on Wednesday.
Crimo faces 117 charges in connection with the shooting, which killed seven and injured more than 30.
Crimo appeared in a prison uniform and mask and repeatedly told Judge Victoria Rossetti that he understood the charges against him.
The 21-year-old is on trial on 21 counts of first degree murder, three for every person killed in the holiday massacre. He also faces 48 counts of attempted murder and 48 counts of aggravated battery, one for each of the four dozen injured.
Prosecutors say Crimo admitted to the rooftop shooting after his arrest.
The prosecution representing Crimo offered no comment Wednesday, citing a policy of not commenting on an ongoing trial.
Authorities have said those injured in the attack range in age from 8 to 80, including an 8-year-old boy who was paralyzed from the waist down.
Crimo faces life imprisonment if convicted.
With Post wires