JACKSONVILLE, Fla. -- Two teens showed no emotion as they admitted to killing their University Christian classmate and pleaded guilty Thursday to second-degree murder.

Charles Southern, 17, and Connor Pridgen, 16, face a sentence of 40 years to life in prison in the shooting death of 17-year-old Makia Coney in February.

Assistant State Attorney Mark Caliel said prosecutors made the plea deals because the teens couldn't receive the death penalty if convicted of first-degree murder, so a first-degree murder conviction wasn't much worse than a second-degree murder conviction.

Caliel said there was a risk that the teens could use the claim of an "accidental firing" to their advantage if they went to trial.

Prosecutors said the two teens killed Coney by shooting her in the head and leaving her body in a ditch off Powers Avenue. Prosecutors said Southern shot Coney once in the head first, then Pridgen shot her once.

Caliel said the killing was "obviously premeditated," and called the teens "simply evil."

Pridgen said he and Southern killed Coney because they wanted to know what it felt like to kill somebody, prosecutors said.

Southern told detectives that he and Pridgen stole the guns because they planned to commit future robberies and said that they needed to know how to fire a gun and see how it felt to shoot somebody if they had to, prosecutors said.

"This was a senseless killing, an act that, frankly, is without reason," Caliel said. "Frankly, it's inexplicable."

Caliel said Southern's mother died several years ago, and he was set to inherit a large trust fund when he turned 18 later this year. Caliel said that makes the killing all the more baffling.

"There was no reasoning behind it," Caliel said. "These two individuals were not indigent. They were not fighting to get money for food or for shelter. They came from good loving homes and had, quite frankly, things available to them that many in our community don't have available to them."

Both teens will be sentenced Oct. 1.