Col. Frank Milstead, director of the Arizona Department of Public Safety, told Greta Van Susteren tonight that they they are now investigating 11 suspected cases of shots being fired at vehicles on Interstate 10 near Phoenix over the past 11 days.

"We've deployed all of the resources of the Arizona Department of Public Safety, along with resources from our federal partners at the FBI, ATF and Phoenix Police Department," Milstead said. "This is job one for my agency, and we will capture whoever this is."

He explained that although no one has been fatally injured, all of the incidents have been "lethal encounters."

"If we don't get a tip that solves this or we don't solve it ourselves, the danger continues to go up."

Milstead added that a $20,000 reward is being offered for information leading to an arrest

Investigators in Arizona are looking into a 10th suspected shooting along I-10, west of Phoenix. 

Police believe in the most recent incident this morning, a projectile - believed to be a bullet - struck a white pickup truck in the rear passenger window.

A picture posted by Fox Phoenix appears to show the window shattered. 

Police are asking for the public's help as they try to track down the suspect or suspects, believing it's only a matter of time before someone is killed.

It's the 10th such incident reported since Aug. 29.

Six of the cases have been confirmed as shootings, with the others described as "projectiles" striking vehicles.

Two suspected shootings occurred yesterday and authorities have offered a $20,000 reward for information.

A 13-year-old girl is the only person hurt so far, sustaining injuries from broken glass.

Watch the clip above.