LONDON, KY. -- Jittery residents living near where a gunman opened fire on a Kentucky highway are taking precautions they never thought would be needed in their rural region, as searchers combed the woods Tuesday hoping to find the suspect.

Brandi Campbell said her family has gone to bed early and kept the lights off in the evenings since five people were wounded in the attack Saturday on Interstate 75 near London, a city of about 8,000 people roughly 75 miles (120 kilometres) south of Lexington.

"We go home and lights go off, and we go upstairs and our doors stay locked," she said.

Several area school districts remained closed on Tuesday while a few others shifted to remote learning as the search for Joseph Couch, 32, stretched into a fourth day.

Searchers have been combing through an expansive area of rugged and hilly terrain near where the shooting occurred north of London.

Less than 30 minutes before he shot 12 vehicles and wounded five people, Couch sent a text message vowing to "kill a lot of people," authorities said in an arrest warrant.

"I'm going to kill a lot of people. Well try at least," Couch wrote in the text message, according to the warrant affidavit obtained by The Associated Press. In a separate text message, Couch wrote, "I'll kill myself afterwards," the affidavit says.

The affidavit prepared by the Laurel County Sheriff's Office said that before authorities received the first report of the shooting at around 5:30 p.m. Saturday, a dispatcher in Laurel County got a call from a woman who told them Couch had sent her the texts at 5:03 p.m.

In response to that call, police initiated a tracker on Couch's cellphone, but the location wasn't received until 6:53 p.m., the affidavit states, almost 90 minutes after the highway shooting.

On Sunday, law enforcement officers searched an area near where Couch's vehicle was found, with a view of I-75. There, they found a green Army-style duffel bag, ammunition and numerous spent shell casings, the affidavit says. A short distance away, they found a Colt AR-15 rifle with a site mounted to the weapon and several additional magazines. The duffel bag had "Couch" hand-written in black marker.

Kentucky State Police Master Trooper Scottie Pennington said troopers had been brought in from across the state to aid in the search. He described the extensive search area as "walking in a jungle," with machetes needed to cut through thickets.

Authorities vowed to keep up their pursuit in the densely wooded area as locals worried about where the shooter might turn up next.

Donna Hess, who lives 10 miles (16 kilometres) from the shooting scene, said she hasn't let her children go outside to play since the shooting.

"I'm just afraid to even go to the door if somebody knocks," she said.

Couch most recently lived in Woodbine, a small community about 20 miles (32 kilometres) south of the shooting scene. An employee of a gun store in London, Center Target Firearms, informed authorities that Couch purchased an AR-15 and 1,000 rounds of ammunition hours before the shooting, the affidavit said.

Joe Arnold, the gun store's manager, declined to comment Monday on details from the affidavit.

Authorities in Kentucky said Monday that Couch was in the Army Reserve and not the National Guard, as officials initially indicated. The U.S. Army said in a statement that Couch served from 2013 to 2019 as a combat engineer. He was a private when he left and had no deployments.

Couch fired 20 to 30 rounds in Saturday's attack, striking 12 vehicles on the interstate, investigators said.

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Schreiner reported from Louisville, Ky.