Authorities investigating the disappearance of 18-year-old Ashley Doolittle identified her body Sunday and determined she died from a gunshot wound to the head.

Investigators for Larimer and Mesa counties said they were working “to file the appropriate charges against Tanner Flores,” Doolittle’s ex-boyfriend. Charges will be filed in Larimer County, according to an official statement released Sunday afternoon.

Flores has been arrested and he will be moved to the Larimer County Jail.

Investigators on Friday found the body near Collbran in Mesa County.

Doolittle was reported missing on Thursday after she didn’t return home as expected. Family members found her car near Lon Hagler Reservoir in Larimer County.

The authorities said they were told Flores was distraught over Doolittle’s recent decision to end their year-long relationship. She was the 2016 Boulder County Fair and Rodeo lady-in-waiting. She attended dances with Flores. She was planning to attend Colorado State University.