High school seniors Ashley Doolittle and her boyfriend Tanner Flores went to prom together in 2015.

Flash forward one year later, and Doolittle wasn't happy anymore, and she told Flores it was over. Days later, she vanished.

Ashley's frantic mother calls the Larimer County, Colorado sheriff's office to report her missing. They then go out looking for the teen and find her car at a local reservoir -- but there was no sign of Ashley.

Even more worrisome, Tanner Flores was also missing, and so was a .22-caliber revolver from his dad's gun cabinet. Detectives ping the teenagers' cellphones and pinpoint a location: the vacant home of Tanner's late grandfather.

SWAT deputies move in and arrest Tanner Flores. A body, later identified as Ashley Doolittle's, is discovered in the back of the truck.

According to police documents, Flores admits to detectives to "shooting Ashley in the head twice because he was angry with her."

Flores is currently in jail held without bond. He is facing two counts of first-degree murder and one count of second-degree kidnapping. Prosecutors have yet to announce if he will face the death penalty.