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Authorities are treating a spate of shootings targeting cars and drivers along Interstate 10 in Arizona as “terrorism,” state police said Tuesday after a ninth incident in 10 days.

A $20,000 reward is being offered for information leading to an arrest, Arizona Director of Public Safety Colonel Frank Milstead told reporters, hours after the passenger window of a car was shattered on Tuesday morning.

"Somebody will get hurt or somebody will get killed if this continues"

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“Any time you have multiple shootings against American citizens on a highway, that’s terrorism. They’re trying to frighten or kill somebody,” he said.

He confirmed officers were investigating nine crimes — five shootings and four other incidents involving some sort of projectile — but stopped short of saying that there was a serial shooter.

“Somebody will get hurt or somebody will get killed if this continues,” Milstead said. “Right now there is a real and continuing threat to Arizona motorists.”

Gov. Doug Ducey urged the public to “stay alert” and said the investigation was “the top priority for the Department of Public Safety and the state of Arizona.”

An off-duty Phoenix police sergeant was driving to work along I-10 Tuesday morning when something hit the passenger side window and shattered it. The sergeant was not in uniform and it does not appear he was targeted, Milstead said.

In one of the first incidents, a 13-year-old girl in the passenger seat of an SUV suffered a cut to her right ear when the vehicle was fired at on August 29.