Ex-college football player on trial for ex-girlfriend's murder

Jurors saw video of police interrogating William Riley Gaul, who is accused of killing Emma Walker, a high school cheerleader, in her sleep.
2:45 | 05/08/18

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Transcript for Ex-college football player on trial for ex-girlfriend's murder
We are back with that college football player on trial accused of killing his ex-girlfriend. Jurors watching video of his police interrogation and a conversation his friend secretly recorded. Amy, I know you're following this for us. Prosecutors say William Riley Gaul stood in his ex-girlfriend's family's backyard and opened fire through her bedroom wall and killed her. His motive, he couldn't get over their breakup, according to the state. This morning, former college football player William Riley Gaul is back in court standing trial for first degree murder, accused of killing his ex-girlfriend, high school cheerleader Emma walker in her sleep. Jurors heard her mother's desperate 911 call after finding her daughter's body. Can you tell me what's going on? She's not responsive. Okay, is she breathing? No. Reporter: Prosecutors say Gaul purposely shot walker through the wall of her bedroom as she slept after the 16-year-old broke up with him. On Monday the law and crime network covering the trial live broadcast prosecutors showing jurors a video of police interrogating him the same day walker's parents found her shot to death in her bedroom. I hope to god I'm not a suspect in her death. Did I say you were? I hope not because -- I wouldn't hurt that girl for -- I would hurt myself before I hurt her. Reporter: Prosecutors also showing the jury this hidden camera video filmed at the request of police by one of Gaul's friends hours after the interrogation who says the football player showed him his grandfather's gun which had been reported missing two days before walker's murder. It just needs to Reporter: Gaul unaware he was being recorded then suggesting walker took her own life. People that understood the situation said she killed herself because of me and her parents or she just killed herself because of her parents. Reporter: Arresting Gaul two hours after this recording just as Gaul was trying to dispose of the weapon. Gaul's attorneys admit their client pulled the trigger but say he didn't mean to kill her. There is no doubt that you will hear some of the most bizarre, reckless conduct of my client. Reporter: But detectives say where he aimed the gun suggests otherwise. The person fired in the location that was consistent with where Emma walker's head would be. Reporter: Prosecutors resting the case Monday as did the defense without calling any witnesses. Gaul has pleaded guilty to reckless endangerment which carries a possible sentence of just 3 to 15 years in prison. Whether he faces life in prison for murder, well, that is now up to the jury, robin. Such a sad, sad story. Her family, thank you, Amy.

This transcript has been automatically generated and may not be 100% accurate.

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