Authorities now say they are investigating at least 11 separate shooting incidents along Arizona's heavily traveled Interstate 10, after they confirmed a bullet hole found in the side of a truck today.
Police had previously announced 12 confirmed cases, which ABC News had reported, but later said that one was not confirmed.
The Arizona Department of Safety said that around 9:40 a.m. today, a hole was reported in the side of a commercial truck-tractor pulling a semi-trailer. Detectives determined that the hole was caused by a bullet strike but they were not able to determine when or where the vehicle was when it was struck.
In another case, now no longer considered a confirmed incident, a driver told ABC News affiliate ABC15 in Arizona today that he was on his way to work around 5 a.m. when he heard a pop from his driver's side rear window.
He pulled into a parking lot and called the state's Department of Public Safety. He said he believed the damage to his window had been caused by a BB gun. Authorities said today they did not believe the window had been struck by a bullet or projectile.
Commuters said they were terrified and some said they were simply avoiding the highway.
"It's pretty scary to think that somebody could be shooting and my daughter could be in the car," Sabrina Dominguez said.
Col. Frank Milstead, director of the state's Department of Public Safety, told ABC News on Wednesday that it was unclear whether all of the incidents are related and also unclear whether all incidents involved bullets.
He classified the incidents as "domestic terrorism," calling the person or people responsible cowards who are putting innocent lives at risk.
"What I say 'domestic terrorism,' I don't know what else you would call it. When you're, you know, inflicting terror on a community, what else is it?" he said recently. "These are bad people trying to do harm to good people."
The department said the incidents dated back to Aug. 29, 2015. Every shooting has happened along a short eight-mile stretch of road that runs through the heart of Phoenix, Arizona. Cars have been hit in both the eastbound and westbound lanes at all hours of the day.
One incident damaged a tour bus; in another shooting, a 13-year-old girl was injured as she rode in a sport utility vehicle. Two shooting incidents were reported Tuesday, including one involving a police sergeant's personal vehicle.
While the Arizona Traffic Operations Center has 19 cameras watching the stretch of highway, 24 hours a day, the footage is never recorded so authorities are unable to go back and review the tapes.
Milstead said his agency had called upon local police departments as well as the FBI and the Bureau of Alcohol, Tobacco, Firearms and Explosives to assist in the investigation.
"We have a hard crime to solve because it's such a large area and there so many different vantage points for someone who wants to do something wrong," Milstead said.
Drivers in the area are being warned to stay vigilant.