M. Spencer Green, File, Associated Press
FILE - In this Jan. 5, 2005 file photo, Chicago Mayor Richard M. Daley points to a .50-caliber assault weapon during a news conference in Chicago. The Illinois Supreme Court is scheduled to announce Thursday, April 5, 2012, whether it is constitutional for Cook County officials to ban assault weapons. The county imposed the ban back in 1993. It has been upheld by trial courts and appeals courts. But opponents think their case gained new strength when the U.S. Supreme Court struck down a Chicago ordinance banning handguns. They hope the state's high court will agree and toss out the ban on assault weapons.

SPRINGFIELD, Ill. — Gun rights advocates scored a victory Thursday when the Illinois Supreme Court decided to let a challenge to Cook County's assault weapons ban proceed, even though two lower courts had tossed it out.

The Supreme Court, in a unanimous ruling, said it wants the trial court to hear evidence on whether assault weapons get the same Second Amendment protections as handguns.

Cook County banned the sale or possession of assault weapons in 1993. The ordinance included details of what constituted an assault weapon and examples of banned guns, but it was aimed at "high-capacity, rapid-fire" rifles and pistols. The law was expanded in 2006 to ban large ammunition magazines.

The ban was challenged by three Cook County residents who said they had perfectly valid reasons to own the prohibited weapons, from hunting to target shooting to personal protection. They argued that the law was too vague and too broad, with little connection to the goal of increasing public safety.

A trial court ruled the ordinance was constitutional, as did the state appeals court.

Then the U.S. Supreme Court struck down a Chicago ordinance that essentially banned handguns. It held that the 2nd Amendment establishes a fundamental right to possess a handgun for self-defense.

The Illinois appeals court reviewed the case in light of the new federal ruling but still found the Cook County ban was constitutional.

But the Illinois Supreme Court says the issue needs a closer look.

The key question is whether high-capacity, fast-firing weapons should be considered ordinary guns that get full Second Amendment protection or treated like machine guns and other special weapons that can be restricted.

In an opinion written by Justice Mary Jane Theis, the Supreme Court said it needs more facts before it can tell whether guns labeled assault weapons "are well-suited for defense or sport or would be outweighed completely by the collateral damage resulting from their use, making them 'dangerous and unusual.'"