(CNN) — Another day, another shooting on a busy stretch of Interstate-10 through downtown Phoenix.
And still no suspects to speak of.
That was the reality Thursday in Arizona, where the Department of Public Safety chief has called the spree of what's now 11 confirmed shootings in 12 days "job one" for his and partner agencies. Still, despite all their efforts to canvass the affected, roughly eight-block area affected, they've had no luck in ending it.
The Arizona DPS reported one more shooting around 9:40 a.m. (12:40 p.m. ET) Thursday — this one a bullet that struck the side of a tractor trailer truck.
Authorities don't know exactly where or when this truck was struck, unlike the others that all happened within a small section on the major highway running through the heart of Arizona's capital and biggest city. Still, they are tying it to the same spate of incidents along I-10 that's occupied them for nearly two weeks.
There have been four such shootings over the past two days alone, including a pair early Tuesday morning and a pickup that was struck by a projectile around 10:45 a.m. Wednesday.
The good news is that none of these shootings — which Col. Frank Milstead said appear to have come from multiple weapons — have been fatal. In fact, there's been only one related injury: A 13-year-old girl whose right ear was cut late last month when a bullet pierced the windshield of the SUV in which she was riding.
But Milstead told CNN that luck may not hold out if this continues, which is why Gov. Doug Ducey referenced the shootings while tweeting that "the safety of Arizonans is our number one priority."
"All of these acts are potentially lethal encounters," Milstead told CNN on Wednesday. "When you're shooting into a moving vehicle with unwitting occupants, (it could be) lethal."
The first shootings were reported on August 29, when bullets hit three vehicles — an SUV, an empty commercial tour bus and a passenger car — as they traveled along I-10.
There were two more shootings over the subsequent two days, then a break until the shootings apparently resumed on Sunday. Since then, two box trucks, two pickups, a passenger car and the aforementioned tractor trailer.
We don't have a suspect in mind ye. But we will find who this is. And hopefully, we get to them before someone is seriously injured or killed.
–Col. Frank Milstead
Milstead said then that some of the motorists didn't immediately realize their cars had been shot, thinking the loud noise they heard was an object on the highway that hit their vehicle.
Arthur Roderick, a former assistant director for the U.S. Marshals, noted the Phoenix shootings appear different from the October 2002 Washington-area sniper attacks that he helped investigate.
For one, multiple weapons would be different from the single gun in the Beltway sniper case. And the latest shootings are more localized and not across several states.
The more confined area could be a plus, with Roderick telling CNN, "They're able to concentrate all their efforts in that one particular area."
That's what authorities are doing in Phoenix by utilizing state police, local departments' SWAT teams, FBI resources and highway surveillance cameras to keep an eye on the area.
As to the motivation and who is responsible, Milstead said, "We don't have a suspect in mind yet.
"But we will find who this is," he added. "And hopefully, we get to them before someone is seriously injured or killed."
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