The man arrested in connection to the Highland Park, Illinois, Independence Day shooting that left seven people dead and dozens wounded has been charged with multiple counts of first-degree murder, authorities said Tuesday.

In addition, police said the suspect may have planned the attack for weeks, and that he wore women's clothing during the incident in order to evade detection. Past encounters with law enforcement, including a threat, were also revealed Tuesday.

Robert Crimo, 21, has been charged with seven counts of first-degree murder, Lake County State's Attorney Eric Rinehart told a news conference Tuesday evening.

"These are just the first of many charges that will be filed against Mr Crimo. I want to emphasize that," Rinehart said, adding that "dozens of more charges centering around each of the victims" are anticipated, among others.