Arizona state troopers are investigating window damage to two vehicles along the Loop 101 Friday.
The Department of Public Safety said shots were not fired and no bullets were found at either incident.
The driver of a blue truck reported damaged to his rear window near Via de Ventura and pulled into a nearby gas station where he contacted DPS.
Authorities said it did not know what caused the damage, but said it wasn't caused by a rock. They also confirmed that it was not caused by a bullet.
A second incident was reported at 19th Avenue. ABC15 went to the area, but was unable to find a scene.
There have been 11 confirmed shootings involving vehicles along Interstate 10 and Interstate 17 since August 29. There has not been a confirmed shooting, however, since September 10, marking eight days without an incident.
State troopers have responded to several reports of broken windshields since them, but most have been determined to be caused by road debris and not connected to the larger freeway investigation.
DPS has placed 16 digital billboards advertising the case and the $50,000 reward along the freeways and passed out thousands of fliers to nearby neighborhoods hoping to reach those who may not be following media coverage.
Arizona Department of Transportation has also placed the DPS Tip Line phone number on all of its electronic signs.