Chicago ? Police found a handgun Wednesday matching the caliber of weapon used in the murders of actress Jennifer Hudson’s three family members, providing a potential break in the case, law enforcement sources said.

The gun was found in an alley just a block from the spot in North Lawndale where Hudson’s 7-year-old nephew, Julian King, was found shot to death and left in the back seat of a white Chevy Suburban.

While it is not uncommon to find guns stashed in public places where street gangs operate, police were intrigued by the discovery because it is a .45-caliber weapon. Also, at least one witness claims to have seen someone driving a vehicle matching the white Suburban drive through the alley and toss something from the window, a source said.

The weapon was being tested to compare with ballistics taken from the murder scenes, police said. Police expected to have some preliminary results today, sources said.