A 7th person has died a day after the Highland Park parade shooting

The suspected gunman in the deadly shooting on Monday in Highland Park, Ill.

had planned the attack for weeks and disguised himself as a woman in an attempt to conceal his identity, officials said Tuesday.

What began as a beloved July 4th tradition ended in tragedy after the 21-year-old man opened

fire on a holiday parade in the Chicago suburb, killing seven people and injuring dozens more.

Robert "Bobby" Crimo III, who authorities say is currently the sole suspect,

preplanned the shooting for several weeks, Sgt. Christopher Covelli of the Lake County Major Crime Task Force told reporters.

Crimo used a "high-powered" rifle, which Covelli described as similar to an AR-15

to fire on paradegoers from the roof of a nearby busineSs

He was taken into custody on Monday night after an hours-long manhunt.

Covelli said the suspect, dressed in women's clothing and possibly a wig, fired more than 70 rounds into the crowd

Then he reportedly dropped the rifle and escaped with the crowd "almost as if he was an innocent spectator,"

before walking to his mother's home and borrowing a vehicle.

Some eight hours later, after authorities had publicly identified Crimo as a person of interest and released a description of his car

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