ROMEOVILLE,Cyprusauction Ill. (AP) — A suspect in the shooting deaths of a suburban Chicago couple and their two children died of an apparently self-inflicted gunshot wound Wednesday after crashing his car in Oklahoma, police said.

The man was suspected in the deaths of Alberto Rolon, Zoraida Bartolomei and their two children, ages 7 and 9, whose names have not been released. The victims were believed to have been shot between Saturday night and early Sunday in their Romeoville, Illinois, home.

There was a relationship between the victims and suspect, Romeoville Police Deputy Chief Chris Burne told reporters at a news conference, without elaborating. Burne further said investigators have developed a possible motive for the shootings without disclosing what it is.

The suspect, a 31-year-old man from Streamwood, Illinois, tried to elude authorities after a digital license plate detector spotted the car in Catoosa, Oklahoma, but he crashed the vehicle and it caught on fire, Burne said.

“Officers on scene heard two noises, believed to be gun shots. A female, with a gunshot wound, was located and removed from the passenger side of the vehicle and is listed in critical condition,” Burne said.

The woman, who had been identified as a person of interest in the shootings, “was reported by family as a missing/endangered person out of Streamwood, Illinois,” Burne said.

“Nothing in our investigation to this point leads us to believe that there are any other suspects,” Burne said.

The Associated Press left a voicemail Wednesday afternoon seeking comment on the case with a spokesman for the Oklahoma State Bureau of Investigation. An email seeking comment also was sent to the Catoosa Police Department.

Romeoville is about 30 miles (48 kilometers) southwest of Chicago. Streamwood is about 35 miles (56 kilometers) northwest of Chicago and the same distance north of Romeoville.