COLUMBUS, OHIO ? Gail Knisley was headed to a doctor’s appointment on a freeway ringing Columbus when a bullet ripped through the driver’s door.

“What was that?” she asked the friend driving; then she slumped forward, fatally wounded.

Authorities said for the first time Friday they had linked Knisley’s death to at least one of nine other reports of shots fired at vehicles along about a five-mile stretch of the same highway — and they said the shooting was not an accident. Police won’t use the term “sniper,” but they say more of the shootings could be connected.

“You just can’t believe someone would be sick enough to be shooting at cars,” Missi Knisley, Knisley’s daughter-in-law, said Friday. “It’s a nightmare.”

The first reported shooting on the southern section of Interstate 270 or in its immediate area was in May. The rest have been in the past seven weeks. The shots have been fired at different times of day, piercing trucks, cars, vans and pickups, shattering windows and flattening tires — and killing Knisley. One of the vehicles hit was a UPS delivery truck.

Authorities have released few details, saying only that tests on the bullets connected Knisley’s shooting on Tuesday to one of the others, though they wouldn’t identify which one. They declined to speculate on the type of weapon used.

Franklin County Sheriff’s Chief Deputy Steve Martin said it was unclear whether one shooter or more was involved.

“I’m not in a position where I can tell you exactly what happened, whether someone was stationary or mobile when any of these shots were fired,” he said.

Authorities on Friday asked whoever was responsible to call the Sheriff’s Office. Martin also said the public should watch for changes in the behavior of friends and relatives, such as missing work or appointments, showing excessive interest in the shootings or changing appearance.

Extra patrols have been assigned to the leg of the highway, also called Jack Nicklaus Highway after the pro golfer from suburban Dublin. The route runs through a sparsely populated area.