UNION GROVE, Wis. - Three Illinois men who were shot to death at point-blank range during a drag racing event in southeastern Wisconsin may have been targeted by a rival gang member but a lack of cooperation has stymied the investigation, sheriff's officials said Monday.

The three were fatally shot as they stood near a concession area in the parking lot of the Great Lakes Dragaway near Union Grove about 7 p.m. Sunday, according to Kenosha County sheriff's officials.

The shooter remains at large, Sheriff David Beth said Monday. A lack of cooperation has made his detectives' work harder, he added.

"Some of the family members, some of the people involved, are not very cooperative with law enforcement. And, that's making it more difficult to investigate this whole thing," Beth said on WTMJ-AM.

Sheriff's Sgt. Mark Malecki said the victims were from the Aurora area in Illinois.

"The victims were known gang members," Malecki said, adding that deputies were investigating the possibility that the assailant was a rival gang member.

Two of the men died at the scene and the third died in an ambulance on the way to a hospital.

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Beth urged any witnesses to the shooting to contact his department.

"A lot of people may not have wanted to come up and talk to the sheriff's department initially because maybe they were afraid someone was going to see them," Beth said. "So what I'm hoping happens is someone who knows what's going on or saw what happened will call us, give us more information and help us catch the individual who did this."

The sheriff's office estimated that more than 5,000 people were at the raceway for an event known as "Larry's Fun Fest." The track's website shows the event included drag racing, tailgating, live entertainment and a car show.

Union Grove is about 25 miles (40 kilometers) south of Milwaukee.