Legislators and activists have derided the weakness of US gun control laws following the Fourth of July mass shooting in which the alleged gunman was allowed to legally purchase weapons despite multiple alarming prior encounters with law enforcement.

On Monday, seven people were killed and more than 30 wounded in Highland Park, an affluent, mostly white Chicago suburb, after the suspect allegedly fired on an Independence Day parade from a rooftop.

Robert Crimo, 21, was subsequently arrested after his gun was tracked with the help of a firearms dealer, and was charged with seven counts of first-degree murder.

He appeared in court on Wednesday in a bond hearing via a video link from jail. Ben Dillon, a county prosecutor, told the court Crimo had confessed to the attack after being apprehended.

Crimo, wearing black, spoke to confirm he did not have a lawyer; he is being represented by a public defender. No plea was entered and the judge ruled he be held without bail. “He does pose, in fact, a specific and present threat to the community,” said the judge, Theodore Potkonjak.

The words echoed those of local authorities in September 2019 when they declared Crimo a “clear and present danger” to the Illinois state police after he threatened to kill his family. Police briefly confiscated a trove of weapons from his house – yet three months later he successfully applied for a gun license, at the age of 19.

According to police statements, on the Fourth of July the gunman climbed to the rooftop and fired on the parade, then drove his mother’s car to the Madison, Wisconsin, area, where he considered attacking another event.

He changed his mind and returned to Illinois, where he was stopped by police at the wheel of the car, said the Lake county major crime task force spokesman, Christopher Covelli.

Police found 83 bullet shells and three magazines of ammunition on the rooftop, Dillon told the court, and a Smith & Wesson semi-automatic rifle, similar to an AR-15, used in the shooting was found at the scene. The suspect had a similar weapon in his mother’s car when arrested, according to county prosecutors.

Before the massacre, Highland Park already had relatively strict gun laws by US standards. In 2013, city officials banned semi-automatic assault riffles and large capacity magazines. Illinois also boasts some of the strongest gun control laws of any state, with mandated background checks for gun purchases, laws limiting gun access to domestic abusers, and a “red flag” law that allows people who pose a danger to themselves and others to be temporarily blocked from purchasing firearms.

Monday’s mass shootings proves that those laws still fall well short of what is needed to curb the spree of mass shootings that has plagued the country, gun control advocates said.

At a Tuesday press conference, the US senator Tammy Duckworth of Illinois said: “Last month, Congress proved that bipartisan compromises on gun safety are possible. Today proved that we can’t stop there.”

Kathleen Sances of the Gun Violence Prevention Pac called on politicians to “act quickly to regulate weapons of war” that make mass shootings increasingly deadly.

Many have also decried the Highland Park shooting as an example of how loopholes within local gun control policies allow offenders to slip through the cracks.

The suspected gunman had two prior brushes with law enforcement that were not flagged in the multiple background checks needed for him to legally purchase multiple guns, Reuters reported.

In April 2019, an emergency call was made after the gunman had attempted suicide, said Covelli.

In September of the same year, police were dispatched to the gunman’s home after he allegedly threatened to “kill everyone” in his family. During that visit officers collected multiple weapons from the gunman’s home: more than a dozen knives, a sword and a dagger.

According to Illinois’s “red flag” law, both instances could have disqualified him from legally obtaining the five firearms he allegedly used during Monday’s mass shooting.

The Illinois state police said, however, that despite the gunman being flagged as a “clear and present danger” following the September 2019 incident and his history of threatening violence, state police closed the case because the gunman did not have a gun owner ID or a pending application to own a gun.

An additional barrier under Illinois law is that police, relatives, roommates or friends must also first ask a judge to seize a person’s guns.

In December 2019, the gunman successfully applied for a gun license when he was 19 years old, with his father sponsoring his application.

State police, who process gun license applications in Illinois, said that “there was insufficient basis to establish a clear and present danger” at the time of his application, reported the Associated Press.

Police said they had no immediate evidence of any antisemitic or racist basis for the attack. The area has a large Jewish community. Investigators were reviewing videos Crimo had posted on social media containing violent imagery.

Authorities have said they plan on seeking additional charges against him, with the Lake county attorney general, Eric Rinehart, promising that the charges would be the “first of many”. If convicted, he could face a maximum penalty of life in prison without the possibility of parole. He is next due to appear in court on 28 July.