The man accused of attacking an Independence Day parade in a Chicago suburb bought his rifle legally, fired more than 70 rounds from a roof and dressed in women's clothing in order to blend into the fleeing crowds afterwards, local officials said on Tuesday.

The suspect, 21-year-old Robert E. Crimo III, was taken into custody on Monday after surrendering to police, hours after the attack on the July 4 parade in Highland Park, Illinois, in which six people were killed and more than 30 people were wounded.

Officials said at a news briefing that he had planned the attack for several weeks, and authorities were still considering what criminal charges to bring. It was not immediately clear if Crimo had a lawyer.

Crimo has distinctive facial tattoos, and appeared to have worn women's clothing on Monday to mask his identity, Chris Covelli, a spokesperson for the Lake County Sheriff's office, told reporters.

"He blended right in with everybody else as they were running around, almost as if he was an innocent spectator as well," Covelli said. The suspect fled to his mother's house nearby, and later borrowed his mother's car.

Officials said they did not know what the motive was for the shooting in a predominantly Jewish neighborhood, but had no evidence that there was any anti-Semitic or racist basis. Investigators were reviewing videos he had made filled with violent imagery.

The suspect used a high-powered rifle for the attack, similar to an AR-15, which he dropped at the scene. He also had a similar rifle in his mother's car, which he was driving when apprehended by police on Monday, and owned other guns at his home, all of which were bought legally in Illinois, officials said.

Highland Park Mayor Nancy Rotering said the community of 30,000 was still in shock from Monday's attack.

"This tragedy should have never arrived at our doorsteps," she told NBC News. "As a small town, everybody knows somebody who was effected by this directly and, of course, we are all still reeling."

The U.S. Supreme Court said last month that there is a constitutional right to carry weapons in public in a ruling that also made it easier for pro-gun groups to overturn modern gun regulations. Since then, the court has thrown out a recent ruling by a lower federal court upholding Maryland's ban on assault weapons.

Congress last month passed its first major federal gun reform in three decades, providing federal funding to states that administer "red flag" laws intended to remove guns from people deemed dangerous.

The law does not ban sales of assault-style rifles or high-capacity magazines but does take some steps on background checks by allowing access to information on significant crimes committed by juveniles.

On Monday, the streets of Highland Park had been decked out in red, white and blue as families watched the annual Independence Day parade. Children waved American flags as parents and grandparents relaxed in folding chairs.

As the parade began rolling through downtown, police said the shooter climbed to the roof of a business using a fire-escape ladder in an alley and then, without notice, opened fire with an assault rifle at the crowd below. He apparently shot into the crowd at random, police said.

21-YEAR-OLD SUSPECT

Rotering, the city's mayor, said she knew the suspect when he was a little boy and a Cub Scout and she was a Cub Scout leader.

"What happened? How did somebody become this angry, this hateful?" she said. "Our nation needs to have a conversation about these weekly events involving the murder of dozens of people with legally obtained guns."

Social media and other online posts written by accounts that appeared to be associated with either Crimo or his rapper alias, Awake The Rapper, often depicted violent images or messages.

One music video posted to YouTube under Awake The Rapper, for example, showed drawings of a stick figure holding a rifle in front of another figure spread on the ground.

Officials had earlier said the suspect was 22, but corrected that to 21 at Tuesday's briefing.

The attack comes as Americans continue debate about gun control and whether stricter measures can prevent the mass shootings that happen so frequently in the United States.