Nicole Bergeron had responded to countless emergencies in two decades as a firefighter and paramedic. But nothing could prepare her for the call when Alexa Bartell was killed by a rock thrown through her windshield.

A man has been convicted of first-degree murder after he and his friends were accused of killing a driver during a night of throwing rocks at cars in Colorado.

Three Denver-area teens cheered each other during a night of throwing rocks at cars — until one of the stones crashed through a windshield and killed a woman, leading to a murder conviction Friday after the trio turned on one another.