Police investigate string of deadly rock attacks on Colorado drivers.

A 20-year-old woman named Alexa Bartell was killed in Colorado after a large rock was thrown at her vehicle, one of at least five similar incidents that occurred over three hours on Wednesday evening. The Jefferson County Sheriff's Office has been unable to identify any suspects associated with the crime spree, including the homicide. Investigators also believe there may have been more than five incidents and have asked victims to come forward. Bartell's employer is offering a $15,000 reward for information about the homicide.