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.

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.

Joseph Koenig was found guilty of all charges related to a fatal rock-throwing incident involving Alexa Bartell. His co-defendants testified against him as part of plea deals.