"The Dexter Killer:" Inside the mind of a murderer

A look at the evidence in "The Dexter Killer" case; plus, newly revealed letters from the man police say wanted to be like fictional serial-killer Dexter Morgan.   

An important piece of evidence was the hockey mask the killer wore when he attacked his two victims in October of 2008. Gilles Tetreault managed to escape the assault, but Johnny Altinger was murdered by the masked man. On October 3, 2008, Canadian man Gilles Tetreault followed directions to a location in Edmonton where he was supposed to meet a woman named "Sheena" he met online. A copy of the directions that Gilles Tetreault was sent by "Sheena." His supposed date had refused to give him the actual address of the house where they were to meet, but instead sent him detailed directions to the location, letting him know that "the garage door will be open for you."  After Gilles  Tetreault entered through the partially raised door into the darkened garage, he felt someone grab him from behind.  Gilles Tetreault quickly realized this wasn't a date, as he came face to face with a man in a hockey mask who shocked him with this stun baton. The masked man took out a gun and ordered Gilles Tetreault to the ground and placed duct tape on his eyes. While Tetreault was on the ground he decided "if I'm going to die, I'd rather go my way than his way." He got up, ripped the tape from his eyes and grabbed the attacker's gun. That's when he discovered it was made of plastic. After a violent struggle, Gilles Tetreault managed to escape from the garage, and quickly drove away. But only a week later, the masked man would find his next target, Johnny Altinger, who wouldn't be as lucky as the first victim.  On October 10, 2008, Edmonton man Johnny Altinger vanished after answering a similar dating ad on the plentyoffish.com website. Concern turned into alarm for Altinger's friends and family when, three days after he vanished, they received this unusual email from Altinger's account. They knew this was highly out of character, so they reported him missing to the police. Johnny Altinger's friends were also able to hand over the directions Johnny had forwarded them before his date. Those directions led police directly to that garage, which turned out to be rented to an aspiring filmmaker named Mark Twitchell.  Mark Twitchell, 29, had rented the garage space to film his movie "House of Cards." The short film featured a killer luring men to a garage and murdering them.  An initial search of the garage uncovered what appeared to be blood spatter, which Twitchell told police came from the "House of Cards" execution scene he was filming. When investigators asked an actor from the film how much fake blood spatter there was from his scene, he responded "None." Luminol tests later revealed excessive amounts of human blood that wasn't visible to the naked eye.  During their investigation, investigators learned that Mark Twitchell was a devoted fan of the Showtime series "Dexter" about an avenging serial killer. Twitchell even posed as Dexter Morgan on Facebook. Police believed Mark Twitchell's garage resembled a scene right out of the Showtime series "Dexter." The garage had plastic sheets covering all the windows, a table with blood spatter, and cleaning supplies laid out. Johnny Altinger's blood was found in the trunk of Mark Twitchell's family car -- a discovery which led to the filmmaker's arrest on Halloween day in 2008. Police believe that Johnny Altinger was hit over the head with this pipe shortly upon entering the darkened garage. He was then stabbed to death. Investigators found a knife in Mark Twitchell's car with blood on both the sheath and knife. The search of the car also led police to discover a deleted file on Mark Twitchell's laptop called "SK Confessions." Despite Twitchell telling the police that the document was a screenplay, investigators would come to find out it was a detailed account of Twitchell's crimes.  Pictured here is the beginning of "SK Confessions," which would become a key piece of evidence in the case against Mark Twitchell. The first lines read "This story is based on true events. The names and events were altered slightly to protect the guilty. This is the story of my progression into becoming a serial killer." From the hockey mask to the lead pipe to the "Dexter-prepped'" garage, the police noticed that line by line the details in "SK Confessions" were aligning directly with the evidence they found at the crime scene. One passage spoke of the killer trying to burn remains in a barrel; police found this burned barrel inside Mark Twitchell's garage. One piece of the puzzle that had the police stumped was the fact that "SK Confessions" spoke of a victim who got away. Find that person, the police thought, and you've proved that "SK Confessions" is real and not the fictional screenplay Mark Twitchell claimed it was. Pictured here is a detective holding up a photo of the hockey mask that authorities believed anyone who had escaped from Twitchell would remember. In June 2010, as Mark Twitchell prepared to take the stand at his trial and argue that he had "accidentally" killed Johnny Altinger in self-defense, he decided to finally disclose the location of Altinger's body. Seen here are Twitchell's handwritten directions on a Google map. The directions led police to a manhole where Twitchell had dumped Johnny's remains.  While preparing to cover the trial for the Edmonton Journal, Canadian investigative journalist and MacEwan University professor Steve Lillebuen began corresponding with Mark Twitchell after receiving a surprise call from the soon-to-be-convicted killer himself.  During their correspondence, Steve Lillebuen pressed Mark Twitchell to explain himself but he wasn't able to get a satisfactory answer from Twitchell.  In the excerpt shown here, Mark Twitchell states, "It is what it is and I am what I am."  Steve Lillebuen writes about these letters in his book "The Devil's Cinema: The Untold Story Behind Mark Twitchell's Kill Room."

He failed to report the scare to the police out of embarrassment. With each day that passed,  Tetreault convinced himself the attack wasn't as serious as he first thought. Read an excerpt of Twitchell's diary Seeing the hockey mask at this police press conference is what prompted Gilles Tetreault to finally come forward.