The man accused of shooting and killing seven people and wounding dozens more at a Fourth of July parade in Highland Park, Illinois, has pleaded not guilty.

Robert E. Crimo III appeared in a courtroom wearing a mask. He reportedly told the judge he understood the charges.

Last month, the 21-year-old was indicted on 21 first-degree murder counts (3 counts for each victim), 48 counts of attempted murder and 48 counts of aggravated battery.

Authorities previously said the suspected gunman admitted to carrying out the shooting.

The multiple first-degree murder charges allege the suspect intended to kill, caused death or great bodily harm and took action with a strong probability of causing death or great bodily harm on the seven people who died.

Authorities have said the more than 30 wounded range in age from 8 to their 80s.

Investigators believe the suspect left parade route, then used his mother's car to driver to Madison, Wisconsin where he reportedly contemplated another attack. He was arrested upon returning to Illinois.