BRIGHTON, Colo. | A Colorado man who told authorities he shot a girl in the head after she hired him to kill her pleaded guilty to second-degree murder Monday as part of a plea agreement.

The deal allowed Joseph Lopez, who had been charged with first-degree murder, to avoid a possible life sentence for the death of 19-year-old Natalie Bollinger, whose body was found in a wooded area north of Denver in late December, one day after she was reported missing.

Adams County District Judge Roberto Ramirez sentenced Lopez, who is 23, to serve a maximum of 48 years in prison.

According to court records, Lopez told police that he replied to a Craigslist ad titled “I want to put a hit on myself” and said Bollinger asked him to shoot her. Lopez told police he tried to change her mind when they first met but eventually he parked the car they were driving in and he shot her.

Bollinger provided the gun, Lopez said.

Prosecutors said Lopez should have called 911 or found help for Bollinger after he saw the post on Craigslist. Bollinger and Lopez texted each other dozens of times before he picked her up and they drove around for “an extended period” before he killed her, they said.

“He didn’t respond as a human being,” Chief Deputy District Attorney Ally Baber said. “He responded as a predator.”

An autopsy report found that Bollinger died of a single gunshot wound to the head. KUSA-TV reports that autopsy also found a “potentially lethal level of heroin” in Bollinger’s body.

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