HIGHLAND PARK, Ill. – Police say he legally purchased a high-powered rifle, disguised himself in women’s clothing, and climbed to a rooftop. Then he is alleged to have opened fire on a Fourth of July parade in a wealthy Chicago suburb, killing seven and wounding dozens.

But the motivation behind the latest U.S. mass shooting – an attack authorities say was “well-orchestrated and carefully planned” for weeks – remains a puzzle to investigators and the shattered community. 

Authorities on Tuesday evening announced they charged Robert “Bobby” Crimo III, 21, with seven counts of first-degree murder. Dozens of other lesser charges are expected. Police did not offer any explanation for the attack.

“We have not developed a motive from him,” said Deputy Chief Christopher Covelli of the Lake County Sheriff’s Office, adding there were no apparent signs the attack was motived by race or religion. “By all indications, it appears Crimo was acting by himself.”

Investigators say immediately after shooting into the crowd, Crimo donned women’s clothing and left behind a rifle on a rooftop, potentially to better blend in and escape.

Police said it appeared Crimo then drove to neighboring Wisconsin after the shooting, but returned and was apprehended nearby “without incident” following a short car chase about 5 miles away from the shooting scene.

Lake County State’s Attorney Eric F. Rinehart on Tuesday evening said the seven counts of first-degree murder are just the first of many charges Crimo will face, an announcement cheered loudly by community members.

Rinehart called Crimo’s attack “a well-orchestrated and carefully planned crime” but declined to elaborate. He said he would ask a judge on Wednesday morning to hold Crimo in jail without the possibility of bail.

“We anticipate dozens of more charges centering around each of the victims – psychological victims, physical victims,” Rinehart said. “These seven counts of first-degree murder will lead to a mandatory life sentence should he be convicted, without the possibility of parole.”