Colorado Teen Allegedly Found with Rodeo Star Ex-Girlfriend’s Body After He Shot Her in the Head

A Colorado teen allegedly found with the body of his ex-girlfriend in the back of his truck has pleaded not guilty to murdering her, PEOPLE confirms.

Tanner Flores, 19, appeared in court in Larimer County, Colorado, on Thursday to enter a plea to his first-degree murder and second-degree kidnapping charges, a Larimer District Attorney’s official tells PEOPLE.

Investigators allege that Flores shot 18-year-old Ashley Doolittle in the head and then drove hundreds of miles with the rising rodeo star’s dead body.

Flores was arrested on June 10, one day after Doolittle’s family reported her missing. Authorities say they had become concerned when she didn’t come home on June 9 and when her car was found abandoned by a lake.

From the beginning, investigators believed Flores was involved in Doolittle’s disappearance. Her family said that Doolittle had recently ended a one-year relationship with Flores, leaving him “upset and distraught,” according to the Larimer County Sheriff’s Office.

Officials soon released an image of his truck, hoping a tip might lead them to the pair.

The following morning, they received a tip that the vehicle was spotted in Mesa County, Colorado, more than 200 miles from Larimer County.

• Want to keep up with the latest crime coverage? Click here to get breaking crime news, ongoing trial coverage and details of intriguing unsolved cases in the True Crime Newsletter.

Flores was found on his deceased grandfather’s property by Mesa County deputies, according to the Loveland Reporter-Herald. Doolittle’s body was allegedly discovered in Flores’ truck wrapped in a blanket, dead from a gunshot to the head, a Larimer sheriff’s spokesman tells PEOPLE. The coroner later found that Doolittle had been shot multiple times, according to the Reporter-Herald.

Flores allegedly shot her while she was riding in his truck, according to court records obtained by the Reporter-Herald. Prosecutors claim he used a revolver taken from his father’s gun cabinet, the paper reports.

In January, when Flores appeared in court for his preliminary hearing, prosecutors presented a videotaped interview with authorities that he gave soon after his arrest, according to the Reporter-Herald. Flores allegedly recounted a shifting version of events around Doolittle’s death.

First, he allegedly said he met Doolittle on the day she died at a reservoir near their homes. Then he claimed he accidentally shot her in his truck while wrestling a gun away from her because she appeared to want to her herself, and then he shot her again to put her out of pain.

Minutes later, however, Flores allegedly changed his story and admitted to authorities that he shot Doolittle as she sat in the passenger seat of his truck, after she glared at him.

About the time Doolittle died, Flores allegedly sent a text from her phone to his saying, “I am not meeting you today,” investigators allege, according to the Reporter-Herald.

On Thursday, Flores’ defense attorney filed a motion for a mental health evaluation. Larimer County District Attorney Cliff Riedel did not object.

Flores is set to appear again in court on April 9. It is unclear how the long the mental evaluation will take. Neither Riedel nor Flores’ attorney could immediately be reached for comment.

Pick up PEOPLE’s special edition True Crime Stories: Cases That Shocked America, on sale now, for the latest on Casey Anthony, JonBenét Ramsey and more.

According to the Reporter-Herald, Doolittle was set to serve as the Boulder County Fair and Rodeo Queen after she was named the lady-in-waiting in 2016. In January, the local rodeo community held a memorial for her. Her friends and family have also attended court hearings for Flores, where they wore commemorative pins of Doolittle in her rodeo outfit, according to the paper.

“It wouldn’t be the same going around to these fairs and rodeos and representing the Boulder County Fair and Rodeo without ,” rodeo friend Sydney Postle told the Reporter-Herald.

“She would have done a great job,” Postle said. “I try to live up to the high standards that she set and just do my best.”

“Ashley’s family is so thankful for the support of the community and the Boulder County Fair and Rodeo Royalty Committee for all they have done to remember Ashley,” her mother told the Reporter-Herald. “This support has made a very difficult time a little bit easier for us all.”