Michael Winter, USA TODAY 6:42 p.m. EDT September 10, 2015

Arizona Department of Public Safety officers inspect a tractor trailer with a bullet hole in the passenger door shortly after it was shot near 67th Ave and I-10 on Sept. 10, 2015 in Phoenix.(Photo: Matt York, AP)

Arizona authorities said Thursday that a bullet hole found in a big rig was the 11th confirmed shooting along Interstate 10 near Phoenix in the past two weeks.

Two additional shootings, one before dawn Thursday near where the truck was hit, were under investigation, the Arizona Republic reported.

The Arizona Department of Public Safety has not announced what caliber weapon or weapons have been used, or whether all of the incidents are connected.

Seven attacks have involved gunfire, and the others "projectiles" that have not been positively identified, a DPS spokesman said in an update Thursday afternoon. BB or pellet guns are suspected in at least three cases, officials said earlier.

Windows have been shattered and doors pierced, but no one has been hurt in the sniper attacks that began Aug. 29. Nonetheless, truckers and motorists are on edge.

In the latest confirmed shooting, a driver found a bullet hole while inspecting his tractor-trailer about 9:40 a.m. PT Thursday at a warehouse off eastbound I-10 at 83rd Avenue in west Phoenix, the DPS said. It's not known when or where the truck was hit.

Just before 6 a.m. a motorist reported one of his windows was shattered, possibly by a BB or pellet, while he drove eastbound near 83rd Avenue, a DPS spokesman told the Republic.

Investigators were also checking a tractor-trailer around 11:30 a.m for a possible gunshot at a truck stop  about 16 blocks away.

A $20,000 reward is being offered for information leading to the arrest of the shooter or shooters.

Investigators inspect a bullet hole found Sept. 10, 2015, in a tractor-trailer parked off Interstate-10 in Phoenix. (Photo: Arizona Department of Public Safety)

In a statement Thursday, Gov. Doug Doucey said he was receiving updates from the head of the DPS, Col. Frank Milstead.

"The safety of Arizonans is our No. 1 priority, and we are committed to apprehending those responsible for these crimes," Doucey said. "I ask all Arizonans to stay alert and contact authorities with any information that could lead to the arrest and prosecution of responsible parties. I assure you, this is the top the priority for the Department of Public Safety and the state of Arizona."

An Arizona Department of Transportation sign gives a hotline number for information on the recent freeway shootings along I-10 in Phoenix. (Photo: Matt York, AP)

The first three attacks were reported Aug. 29, two involving passenger vehicles and one an empty tour bus. Over the next two days, a car and a pickup truck were struck by bullets. On Sunday, a box truck and a car were hit by gunfire, and Tuesday another box truck and a pickup were hit by projectiles. Wednesday, another projectile shattered the rear passenger window of an eastbound pickup near 39th Avenue.

The attacks echo a 15-month shooting spree that killed eight people and terrorized the Phoenix area in 2005 and 2006.

Dale Hausner and Samuel Dieteman were convicted of firing shotguns and rifles at 25 people and various animals while out joyriding. At least 10 dogs and horses were also killed.

Hausner committed suicide in prison two years ago, and Dieteman is serving a life term.

Read or Share this story: http://usat.ly/1EZqyZU