In the early morning hours after Harris County Sheriff’s Deputy Darren Goforth was murdered, Shannon Miles sat in an interrogation room chair for what would be a grueling interview with homicide detectives.

They methodically tried to pry information out of then-accused cop killer. But at every turn, the 30-year-old Miles kept denying any involvement.

Detective: "The guy I'm looking for shot a gun."

Miles: "I ain't shot no gun. I hadn't shot no gun."

Miles denied he was at the gas station in Northwest Harris County where Goforth was shot 15 times Aug. 28, 2015. It was an execution-style killing that shook even the most veteran cops to their core.

"I don't recall another incident this cold blooded and cowardly,” said then-Harris County Sheriff Ron Hickman.

Related: Shannon Miles to serve life without parole for murder of Deputy Goforth

In the interrogation room, detectives showed Miles snapshots of the gas station surveillance video.

"That's not even, that's not, that's not me, man. I don't think that's me," Miles said looking at the photo on the detective’s phone.

He denied even knowing anything about the crime that had occurred.

"I didn't even know the dude got shot, you know what I mean?” Miles said. “This is news to me, you telling me he got shot."

At one point, investigators called in a crime scene technician to take photos of Miles for a lineup. His hands were also tested for gun powder residue.

A couple miles away, other detectives were at the home of Miles’ mother. They searched his red pick-up truck that matched the crime scene surveillance video, and also found a gun in the garage.

Detective: "The gun that you voluntarily told us was in your garage was used to kill that officer. Could you explain that for me?”

Miles: “No. I wouldn't be able to explain any of that.”

Miles stuck to his story that he was never at the scene of the crime and was out shopping with his mother.

"The only thing I can tell you is I was at work, I got off, I went home, I showered,” Miles said. “My brother seen me at home, I rolled up with my mother, it couldn't have been me."

But detectives said the surveillance video, the matching truck, and positive ballistics evidence added up to a mountain of evidence that could not be explained by coincidence.

“You’ve got a better chance of picking a winning lotto ticket then you do of coming up with all of those coincidences,” one detective said.

In their search for motive and meaning, detectives questioned Miles’ mental state of mind. They asked if he had any “demons” or ever heard “voices,” but he replied "no." They also asked if Miles had an ax to grind or was angry at police. Miles did talk about his past run-ins with the law.. but nothing that spoke of revenge in any way.

Throughout the interrogation, Miles appeared cooperative and coherent.

"I'm telling you what happened. I'm giving you my side of the story. That's all I can give,” Miles said.

The then-accused cop killer never admitted to anything. His defiance clearly frustrated detectives, who changed their tone after hours of grilling the suspect in the interrogation room.

“How can anybody look at you than anything other than a monster that would kill a police officer?” Sgt. Craig Clopton asked Miles.

Clopton used the term “monster” 15 times during his line of questioning. He was later fired from the Harris County Sheriff’s Office for having sex with a witness in the case.

“What I do know is that you shot the officer. You drove that truck,” Clopton told Miles. “What I want to know is what led to that?”

Detectives searched for motive and meaning, but never were able to pry either out of the murder suspect.

“I told you everything I can tell you,” Miles said. “That’s it. I mean, it don’t make sense for me. Senseless.”

But the senselessness appeared to later sink in when investigators left Miles alone in the interrogation room. He pulled at his polo shirt and buried his head underneath.

Two years later, Shannon J. Miles stood before a judge and pleaded guilty to capital murder.

Prosecutors and defense attorneys both said it was a history of mental illness that played a large factor in the plea deal Miles agreed to for a sentence of life without parole.