Apr. 21—Colorado officials are offering a $17,000 reward — 15,000 of which from a private business donor — as they try to gather more information on a rock-throwing spree that reportedly ended with the death of a 20-year-old woman.

According to a release, 20-year-old Alexa Bartell, of Arvada, was driving north in the 10600 block of Indiana Street at 10:45 p.m. Wednesday when she was apparently killed by a large rock thrown at her vehicle from another vehicle or the side of the road.

Investigators said Bartell was on the phone with a friend at the time when her line went silent. The friend tracked Bartell's phone and found Bartell dead inside her vehicle, which had gone into a field off the road.

According to the release, investigators believe the homicide is related to a string of similar incidents overnight.

That includes two incidents at about 10:30 p.m. Wednesday near McCaslin Boulevard and S. Indiana Street at the entrance to the Rock Creek neighborhood in Superior. Two different vehicles were hit by rocks, with one driver reporting minor injuries after the rock went through the vehicle's windshield.

Incidents were also reported at 10:04 p.m. Wednesday in Westminster at 100th Avenue Simms Street and at 10:26 p.m. in Arvada near Colo. 72 and Colo. 93.

Investigating agencies — including the Jefferson County and Boulder County sheriff's offices, Arvada Police and Westminster Police — were trying Thursday to locate a pickup truck that was initially believed to be connected to the case.

But officials said late Thursday night that they spoke with the owner of the vehicle and no longer believe they were involved.

Officials are still hoping to locate any witnesses to the incidents or video surveillance footage from houses and vehicles in the area. Investigators also believe there may be other incidents that have not yet been reported.

Anybody with information about the incidents or video evidence is asked to call the Jefferson County sheriff's tip line at 303-271-5612.

Colorado Crime Stoppers is offering $2,000 of the $17,000 reward for information. Tips can be called in to 720-913-STOP (7867).