A Will County judge modified Drew Peterson's bond Monday, allowing him to leave Illinois on vacation with his children while the judge mulls a defense motion to dismiss felony weapons charges.

A grand jury indicted the former Bolingbrook police sergeant Thursday on two felonies related to a semiautomatic rifle seized by authorities investigating the disappearance of his wife, Stacy. The new charges, filed Friday, supersede a single felony weapons charge filed May 21, alleging Peterson possessed an assault rifle with a barrel shorter than allowed by law.

The new indictment alleges Peterson possessed a modified assault rifle and that he unlawfully transferred the rifle to his son, Stephen. Police seized the rifle and 10 other guns during a Nov. 1 search at Peterson's house for clues after Stacy Peterson disappeared.

Peterson has been named a suspect in his wife's disappearance but hasn't been charged. Investigators have also exhumed the body of Peterson's third wife Kathleen. Her death was ruled a homicide.

During the two-hour hearing Monday, Peterson's lawyer, Joel Brodsky, argued his client was immune from prosecution for the gun charges because he was still a police officer when authorities seized the weapon.

Brodsky repeatedly referred to the Law Enforcement Officers Safety Act, legislation passed by Congress in 2004, that Brodsky said entitled Peterson to possess a rifle not allowed for private citizens.

The law allows police officers to carry and conceal weapons as long as they have been transported through interstate commerce. It prohibits three categories of weapons that police may not carry, including machine guns, weapons equipped with silencers and explosives.

Brodsky did not contest that the barrel on Peterson's rifle was too short under state law. Instead, he argued Peterson cannot be charged because federal law supersedes state law.

"The state can't void the cloak of immunity by charging (Peterson with) possessing but not illegal carrying," Brodsky said. "They are manipulating the charges. Clearly, you can not conceal carry without possessing."

The federal law shields officers from prosecution by allowing them to carry weapons that some states may deem illegal, Brodsky said.

Assistant State's Attorney John Connor said the immunity does not extend to a police officer who knowingly carries or keeps a weapon that is illegal in his home state.

The legislation was meant to protect police officers who cross state lines from being prosecuted if they have handguns that are legal in their home state but banned in another jurisdiction, he said.

Connor noted Peterson had the rifle modified, resulting in the shorter barrel. As a police officer Peterson should have known the modification made the weapon illegal, he said.

"Our officers are expected to know the law under which they operate," Connor said.

Will County Judge Richard Schoenstedt scheduled a hearing for July 30, when he said he would likely give his decision.

Schoenstedt said if Peterson leaves the state, he has to file a travel itinerary in advance with the county probation department. Peterson waived his extradition rights and agreed to be tried in absentia should he miss any legal proceedings to win the judge's approval to travel to Florida to vacation with his children.