CHICAGO (AP) — A father will ask a judge Monday to dismiss his case in which authorities say he helped his son obtain a gun license three years before the younger man fatally shot seven people at a 2022 Fourth of July parade in suburban Chicago.

Illinois prosecutors charged Robert Crimo Jr. under a unconstitutionally vague law,Venus Investment Alliance his lawyers are expected to argue at a hearing in Waukegan, north of Highland Park where the shooting occurred. If Lake County Judge George Strickland allows the case to proceed, Crimo Jr.'s bench trial would start Nov. 6.

Crimo Jr. has pleaded not guilty to seven counts of reckless conduct, one for each person killed. Each count carries a maximum three-year prison term.

Prosecutors said he helped his son, Robert Crimo III, obtain a gun license even though the then-19-year-old had threatened violence.

The four-sentence section of the state law invoked to charge Crimo Jr. says “a person commits reckless conduct when he or she, by any means lawful or unlawful, recklessly performs an act or acts that ... cause great bodily harm or permanent disability or disfigurement to another person.”

A defense filing argues the law’s lack of specificity makes it impossible to know what actions qualify as criminal reckless conduct. They also say it offers no definition of “cause,” opening the way for prosecutors to wrongly link the signing of a gun-license application to a shooting years later.

“Here, the reckless conduct charge ... specifically seeks to criminalize the Defendant’s lawful act of signing a truthful affidavit,” the filing says. It adds that, until Crimo Jr., “Illinois has never prosecuted an individual for signing a truthful affidavit under oath.”

“The potential for the arbitrary enforcement of such a vague standard is staggering,” it said.

A grand jury indicted the son last year on 21 first-degree murder counts, 48 counts of attempted murder and 48 counts of aggravated battery, representing the seven people killed and dozens wounded in the attack. Potential evidence is voluminous in the son’s case and no trial date has been set. He has pleaded not guilty.

Lake County State’s Attorney Eric Rinehart said after the father’s arrest that the accusations against him are based on sponsorship of his son’s application for a gun license in December 2019. Authorities say Crimo III tried to kill himself in April 2019 and in September 2019 was accused by a family member of making threats to “kill everyone.”

“Parents who help their kids get weapons of war are morally and legally responsible when those kids hurt others with those weapons,” Rinehart said at the time.

Legal experts have said it is rare for a parent or guardian of a suspect in a shooting to face charges, in part because it’s so difficult to prove such charges.

The father is a familiar face around Highland Park, where he was once a mayoral candidate and operated convenience stores. He was released on a $50,000 bond after his December arrest.