The video showing the interrogation of convicted sex killer Russell Williams is a window into the way skilled investigators use psychology to extract confessions, experts say.

A condensed video of the 10-hour interrogation that pried loose a confession from the former CFB Trenton commander was shown in a Belleville, Ont., court this week.

OPP Det. Sgt. Jim Smyth, a veteran investigator, is the other man seen in the video.

He is the detective who was tasked with confronting Williams about his crimes.

The video begins with Smyth telling Williams why he has been called in to speak with police.

Smyth speaks in a friendly tone and tells Williams that he appreciates his co-operation in the matter.

At this stage, Williams flashes an occasional grin and chews gum.

Mark Mendelson, a retired homicide investigator, said Williams has the air of someone who does not think he is about to get caught.

"He just thought he was going to outsmart everybody else and talk his way right out of it," Mendelson told CTV Toronto after viewing the video of the confession.

Smyth gets down to business by slowly revealing to Williams what police have found out about the murders of Jessica Lloyd and Cpl. Marie-France Comeau, as well as the attacks on two women from Tweed, Ont.

Several hours pass by and Smyth makes it increasingly clear there is heavy suspicion surrounding Williams.

"We need to have some honesty, okay? Because this is, this is getting out of control really fast, Russell. Really fast," Smyth tells Williams, shortly before he confesses.

The fact that Smyth calls him "Russell" is significant, said Mendelson, because it puts the detective and Williams on an even playing field.

"That hierarchy's gone now, that special status is gone. So that brings him down," said Mendelson.

A killer cracks

Retired OPP investigator Dave Perry said it is compelling to watch as Smyth calmly presses Williams on his links to the crimes.

"I just watched as they peeled the layers away and started presenting evidence, and found it quite fascinating the way it sort of segued into a confession," Perry told CTV's Canada AM in a recent interview.

Perry said you can see the growing discomfort registering on Williams' face as he is confronted with more and more damning evidence.

The bootprint and tire tracks at a murder scene match his boots and personal vehicle. The attacks occurred in areas where Williams lived and frequented. Comeau was also a member of the Canadian Forces who worked on the same base as Williams. The looming DNA test that will inevitably identify him as being a killer.

Perry said the killer's body language reveals that his defeat is beginning to sink in.

"The non-verbals are ringing loud and clear on this one. He is leaning forward, he's actually nodding in agreement with everything that's being said to him," he said.

Williams hunches his shoulders. He stays silent for long periods of time.

It's at this point where Williams "is absorbing everything that's just been said to him and that's for the first time that he knows that he's caught," Perry said.

Mendelson said it's a moment where Williams realizes he has "nowhere to go."

Eventually, Williams reveals that he is concerned about the fact the OPP will soon be "tearing apart my wife's brand new house."

Smyth says there is a way to minimize the pain, which starts "by telling the truth."

Soon after, Williams tells Smyth to get a map. Over the next few hours he admits to the murders and rapes he committed while holding down his day-job as the commander of Canada's largest air force base.

A successful strategy

Experts who have watched the video are impressed with the way Smyth handled the interrogation.

"It's a smart man, outsmarted by a smarter man," OPP Det. Insp. Chris Nicholas told reporters in Belleville earlier this week.

Perry, who previously worked on cases with Smyth, said the OPP investigator used a "classic way of presenting evidence" during the interrogation.

"When the first piece of evidence was presented, (Williams) started to say: ‘I don't understand' and all that," said Perry.

Perry said that's when Smyth takes control and repeatedly suggests that the evidence points to Williams as the killer.

Brent Snook, a forensic psychologist and professor at Memorial University, said Smyth's interview was highly professional and non-confrontational in nature. He used rational arguments to convince Williams that he had been caught.

Snook said this type of approach relies on having an officer build a rapport with the suspect and listen carefully to what is said.

In the Williams interview, it became clear that his relationship with his wife was very important, which Smyth keyed into when he offered him the chance to minimize the impact on his spouse.

Retired homicide investigator Steve Roberts told The Canadian Press that investigators such as Smyth always try to find a suspect's weakness and use it to their advantage.

That's why investigators will typically study up on their subject before entering the interrogation room, carefully reviewing the items found in police searches.

They look for a way to open up a suspect and to get them to start talking.

Roberts said he once "cracked a guy from the Hells Angels because in his wallet were pictures of his dog and his dog was the most important thing in his life."

But he said some suspects need to see hard evidence before they will open up.

That suggests that Smyth had two possible levers to pull in the Williams interrogation: a growing mountain of evidence and Williams' concern about his wife's reaction to the news that she was married to a killer.

Elliot Leyton, a Memorial University professor who has authored several studies on serial killers, said Williams "is intelligent enough to know that they had him."

He suspects Williams would have weighed the judicial process that lay ahead when making his decision to confess.

"He didn't want any more public shaming than he could avoid, I assume, and therefore he made a decision to bail out now, avoid the trial, avoid the public shaming, avoid the whole excruciating process of humiliation that was set up for him," Leyton told The Canadian Press this week.

With files from The Canadian Press