A suspect in the shooting deaths of a suburban Chicago family died following a fiery crash in Oklahoma, along with a passenger, police said.

Nathaniel Huey Jr., of Streamwood, Illinois, tried to elude authorities after a digital license plate detector spotted him Wednesday in Catoosa, Oklahoma, but he crashed the vehicle, and it caught fire, police said. It’s unclear whether the crash, or gunfire officers heard at the crash scene, killed him and the woman who was his passenger.

Huey, 32, was suspected in the deaths of Alberto Rolon, Zoraida Bartolomei and their two sons, ages 7 and 9. They were believed shot between Saturday night and early Sunday in their home in Romeoville, about 30 miles (48 kilometers) southwest of Chicago.

Police were asked to check on the family Sunday night after one member did not show for work that morning and phone calls went unanswered, police said.

The names of the children have not been released. Three dogs were also found dead, news outlets reported.

A GoFundMe page created to raise money for helping the Rolon-Bartolomei family with funeral expenses describes the couple as hard-working people who had just bought their first home.

“Their kids were the sweetest most innocent angels who could hug your worries away,” the organizers said.

The victims and Huey had a relationship, Romeoville Police Deputy Chief Chris Burne told reporters at a news conference, but did not elaborate. Investigators believe they know Huey’s motive but have not disclosed it.

Officers who were at the crash scene “heard two noises, believed to be gunshots,” and both the man and the passenger had a gunshot wound, Burne said at Wednesday’s news conference. An Oklahoma state investigator said that the passenger was a woman and that the nature of their relationship was being investigated.

The Oklahoma State Bureau of Investigation said in a statement Wednesday night on Facebook that did not include Huey’s name that the driver was pronounced dead at the crash scene after the vehicle struck a concrete barrier. His passenger later died at a hospital, it said.

The Oklahoma medical examiner’s office will identify them and determine their cause of death, the statement said.

The woman, described as having a relationship to Huey and 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. There are no other suspects at this point, he said.

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

Cristiana Espinoza, 25, said she filed the missing person report Tuesday afternoon for the woman, saying she had been concerned about her safety.

“I know she left with him willingly about 4 p.m. Tuesday,” Espinoza said in a telephone interview. “When I saw her, she was scared. She was crying. I was in contact with her. We knew where she was. I was begging for her to come home. I honestly feel she left to protect her family.”

Espinoza said she was acquainted with both Huey and the woman. She did not discuss the nature of their relationship.

Hunter McKee, spokesperson for the Oklahoma State Bureau of Investigation, said the agency was called in to help the Catoosa Police Department after the suspect’s vehicle was spotted by a digital license plate detector.

Catoosa officers saw the suspect’s vehicle, but no one was inside, McKee said. As officers watched it, two people got in and drove away. Police began pursuing it, and the driver crashed into the barrier.

The family’s death marks the 35th mass killing in the U.S. this year, according to a database maintained by The Associated Press and USA Today in partnership with Northeastern University. A total of 171 people have died in those killings, which are defined as incidents in which four or more people have died within a 24-hour period, not including the killer — the same definition used by the FBI.

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Ken Kusmer reported from Indianapolis and Corey Williams from West Bloomfield, Michigan. Contributing to this report were Associated Press writer Lisa Baumann in Bellingham, Washington, and AP news researcher Jennifer Farrar in New York.