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. Investigators identified the victims to CBS affiliate WDJT-TV as 30-year-old Khalid Howard, 26-year-old Derek Edwards, and 30-year-old David Watson.

The shooter remains at large, Sheriff David Beth said Monday. Beth said the victims were members of a gang in Illinois, but he didn't know a motive in their slayings. A lack of cooperation has made his detectives' work harder, he added.

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"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. Beth said the father of one of the deceased is a high-ranking gang member in Illinois.

Two of the men died at the scene and the third died in an ambulance on the way to a hospital. Beth said he wasn't sure why the shooting happened at the raceway.

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 said thousands of people including families and children 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.

Beth described the scene as "chaotic." He said the gunman was seen fleeing through the crowd.

Union Grove is about 25 miles south of Milwaukee.