Arizona police have confirmed 11 attacks in a string of shootings in the last two weeks that have terrorised drivers on Interstate 10 freeway. Governor Doug Doucey pleaded with residents to "stay alert and contact authorities with any information that could lead to the arrest and prosecution of responsible parties."

NBC News reported that authorities have not ruled out the possibility that they could be dealing with more than one gunman. A bullet hole in the side of a tractor-trailer was reported on 10 September, with police investigating another, possibly related, report as well.

Ten other shootings have been reported on Arizona's Interstate 10 in less than two weeks, NBC News reported. Seven of those shootings have been identified as bullet strikes, while the other three were unspecified projectiles.

In all 10 incidents, only a 13-year-old girl was injured by glass when it was shattered by a bullet, police said. Another victim, Robert McDonald, told NBC News that he barely missed being grazed by a bullet when his empty tour bus was shot at. McDonald said he would have been grazed in his shoulder if the shot had been a bit more powerful. "And if I would have moved my head," he added. "I would have got hit."

According to NBC News, police do not have a suspect or even a description of the suspect's vehicle. Colonel Frank Milstead, director of the state's Department of Public Safety, referred to the multitude of attacks as "domestic terrorism crimes."

"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, according to ABC News. "These are bad people trying to do harm to good people." Milstead said referred to the individual or individuals involved as cowards who were putting lives as risk.

ABC News reported that although the Arizona Traffic Operations Centre has 19 cameras watching the highway at all hours of the day, the footage is not recorded, which means investigators cannot go back to review the footage. Milstead told reporters that he has asked local police departments, the FBI and the Bureau of Alcohol, Tobacco, Firearms and Explosives to help with the investigation.