Warning: The videos that accompany this story contain graphic descriptions of violence.

By the time Cpl. James Morton sat down to interrogate Mark Lindsay, the RCMP had collected a small mountain of evidence against him.

Lindsay, 29, is on trial in Red Deer, Alta., charged with second-degree murder in the death of his girlfriend, Dana Turner.

The son of former Edmonton police chief John Lindsay admits to killing Turner but has pleaded not guilty. His lawyer, Kent Teskey, is expected to argue Lindsay is not criminally responsible due to his mental state at the time of the offences.

In the small cinder-block interview room in March 2012, Morton told the man over and over again they knew he was guilty.

"There is absolutely no doubt that you're responsible," Morton said. "I know what you did to her and you know what you did to her."

But even an ironclad case is made stronger when the accused admits guilt.  

It took hours of relentless, patient grilling, but Morton finally got a full confession. 

Almost four hours into that police interview, Lindsay admitted that he attacked Turner in August 2011, that he stabbed her in the eye with a pencil, then strangled her with a shoelace.  

WARNING: Graphic/Disturbing content. Mark Lindsay's confession1:51

The interrogation dance that led up to that confession was fascinating.

It began with the corporal anticipating Lindsay's paranoid tendencies.  

Morton brought along two breakfast sandwiches to the interview room. He told Lindsay he did that "so you could pick the one you want. And I, I'll eat the other one."

Lindsay was hostile at first. But the veteran officer never strayed off the good-cop script.  

He never raised his voice. He never swore. He tried to convince Lindsay he understood him and cared about his well-being.  

"The fact that things have happened to you in your life that have been difficult for you, I care about that," he said. "And I care about you and what happens to you."

The 29-year-old fidgeted on the straight black chair in the corner. He got angry when the officer wouldn't let him tell the story his way. At one point, he began to pace back and forth in the tiny room, stuffing paper into his ears. Morton asked him to sit down.

"No, you're just harassing me," Lindsay said.

"Well, no, I'm not," Morton replied. "I'm talking to you in a very calm and reasonable voice."

Lindsay rambled at length about his fears, about an imagined group of serial killers he called Healers. He tried to discuss everything but the woman he murdered.  

Morton told Lindsay he understood why.  

"I know that you crave attention and you absolutely demand to be in control," Morton said.  

"I know that when you are being approached with facts and realities that you don't want to admit to or take responsibility for, you will change the subject … and then all of sudden, we're gone into the toolies because you're not in control." 

Two hours and 10 minutes into the interview, Lindsay opened up about meeting Turner when they were both patients at Alberta Hospital. He admitted he liked her and said she felt like they were "soul mates."  

Mark Lindsay describes meeting Dana Turner1:30

Morton rewarded Lindsay with encouragement and a verbal pat on the back.

"Mark, I can only imagine how hard it is for you to open up about this stuff, and how emotional you are about your feelings for her. All I care about is the truth," he said. 

It was a turning point between the two men. Even though Morton still had to work hard to keep him on track, Lindsay wanted to help the RCMP officer understand "the truth."  

He admitted he stabbed Turner in the head with a paring knife shortly after they were both released from Alberta Hospital.

WARNING: Graphic/Disturbing content. Mark Lindsay describing earlier stabbing incident1:28

Morton told him, "Thank you for that, Mark. Thank you for telling me that."  

Lindsay replied, "I'm not a criminal." Then he sobbed with remorse for stabbing his girlfriend.

"I was worried sick. I just regretted it and I wanted nothing more than to talk to her and to try to continue the relationship," he said through his tears. "Because it was kind of like the saying 'You don't know what you have until it's gone.'"

Showing signs of remorse for stabbing Dana Turner1:17

When Morton testified this week at the murder trial, he told court the interview with Lindsay went exactly the way he expected it would. He said he was prepared for the rambling, the misdirection, even the hostility.

Morton said it was not even close to the most challenging interrogation he has ever done.  

But it may be one of the longest. 

After Lindsay had answered almost every question posed by the corporal, Morton asked him, "How do you feel about talking to me?"

"It's awkward — upsetting but exciting because I can get it off my chest," Lindsay admits. "Because it's been trapped inside of me for a long time."