The 911 dispatcher heard a woman's screams, and then the gunshots.

Police officers who raced to the scene about 10:30 a.m. Saturday found the bodies of Jamie Joiner, 30, and her sister Jessica Joiner, 34, outside a home in rural Madison County, Illinois.

Both had been shot "in the head and neck region," Madison County Chief Deputy Sheriff Jeff Connor said at a news conference on Sunday.

Describing the 911 call to Collinsville police that was forwarded to his agency, he said: "You could hear a female in the background screaming, and then a couple of what appears to be gunshots in the background."

Within 45 minutes authorities had identified the suspect as Adam Cobb, 32, who shared the residence with Jamie and was believed to be on the run.

They later learned that Jamie and Adam had broken up, Connor said. "She had notified him that she was going to be moving, and we believe that her sister flew in from California, possibly the day before, to assist her in moving," he said.

"They pulled up with a U-Haul, a rented U-Haul, and a car, and at some point a disturbance took place, and Mr. Cobb shot both females," he said.

"He also shot a family dog, which was deceased at the scene," he said.

A phone found near her body led investigators to surmise that Jamie had placed the 911 call.

More than two hours later, following an alert to neighboring jurisdictions and with the aid of cell phone tracking, a vehicle with Cobb at the wheel was spotted in adjacent Montgomery County. When Cobb refused to pull over, a 40-minute pursuit began that followed the vehicle into Christian County, where it became "partially disabled," police said.

When Cobb got out, authorities said, he allegedly pointed a gun toward a tenured Illinois State Police trooper with 26 years' experience, who fired his own weapon and struck the suspect.

A "large calibre" gun found with Cobb is believed to be the same one used to kill the sisters, Connor said. "Forensics will later determine if it was, in fact, the same weapon, but the evidence suggests that it is," he said.

Cobb was taken to a hospital with life-threatening injuries and pronounced dead at 4:40 a.m. Sunday.

His neighbors expressed shock at the events.

"He helped everybody all the time, and I still can't get over it," said Renee Crouch, who lives about a mile from Cobb's home and said that he often cut her grass for her, reports KSDK.

Another neighbor, Ben Sharp, told the outlet: "I couldn't ask for a better neighbor."

On Sunday afternoon, reporters at the crime scene still saw the U-Haul truck in the driveway, with its rear door still open, according to KSDK.

Connor says investigators do not know which of the sisters was shot first. There were no witnesses.

"Some of these things we'll never know," he said. "This is pretty much a domestic situation that ended in a tragedy. Our thoughts go out to all these families, the Joiner family and the Cobb family. They're both going through a lot right now."