11 shootings in 11 days along busy Phoenix highway

Eleven shootings, 11 days, all along one small, busy stretch of Interstate-10 through downtown Phoenix.

And no suspects, and no end in sight -- yet.

Fresh off two more shootings Wednesday, the head of the Arizona Department of Public Safety called ending this spree "job one" for his and partner agencies. But to do so, he said, the public may need to help.

"Somebody is very aware of who this is," Col. Frank Milstead said. "... There should be no benevolence for this person, or apathy. This is a cold-blooded crime. This person is a coward."

No one has been killed in these shootings of vehicles in the Arizona capital. There's been only one 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, the DPS said. She was treated at the scene.

"All of these acts are potentially lethal encounters," Milstead said. "When you're shooting into a moving vehicle with unwitting occupants, (it could be) lethal."

4 shootings in past 2 days

The first shootings were reported late last month, when projectiles hit a windshield, the sides of vehicles and a headlight over three straight days.

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.

But concerns that this might be something more than random have mounted in recent days. That includes shootings -- one at a vehicle going eastbound, another at one going westbound -- around 5:20 a.m. (8:20 a.m. ET) Tuesday morning.

Then came two more incidents Wednesday, according to Milstead.

All the shootings over the past two weeks came in one eight-block stretch. But they weren't all identical: Milstead noted the latest ones "seemed to have a different MO than the ones before."

And he referred to what was fired as "projectiles," adding, "I think we have a number of different weapons involved, but we're still trying to determine that."

Official vows, 'We will find who this is'

Arthur Roderick, a former assistant director for the U.S. Marshals, noted the Phoenix shootings appear different than the October 2002 Washington-area sniper attacks that he helped investigate.

For one, multiple weapons would be different than 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."