Mark Twitchell told an American Facebook friend that he "crossed the line" days after police say a man was killed in a south Edmonton garage.

"Suffice it to say that I crossed the line on Friday and I liked it," Twitchell wrote to Renee Waring in a Facebook message on Oct. 14, 2008.

The Crown alleges Twitchell, 31, killed and dismembered Johnny Altinger, 38, on Friday, Oct. 10.

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Renee Waring is shown giving testimony at Mark Twitchell's first-degree murder trial on March 30, 2011. (CBC)

Twitchell, an aspiring filmmaker, had a Facebook profile under the name of Dexter Morgan, the fictional lead character in a TV show about a serial killer who murders other serial killers, the jury at his first-degree murder trial was told Wednesday.

"I am a fan of the TV show Dexter and the books. I've watched every episode," Waring said in her testimony by video link from Cleveland, Ohio.

Waring testified she first became Facebook friends with Twitchell in September 2008 and exchanged more than 40 Facebook messages with Twitchell from Sept. 29 to Oct. 27, 2008.

A day after she became friends with him on the social media site, he told her his name was Mark. Shortly afterwards, he sent her pictures and told her about his movies.

Dump body 'Dexter style,' woman advised

In one exchange, Twitchell writes: "We all have a dark side, some darker than others and you're not the only one to relate to Dexter," Twitchell wrote. "It sometimes scares me how much I relate."

Waring said the pair began discussing "dark thoughts" and "dark fantasies" with each other, including one she had of killing her ex-husband's new wife.

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Mark Twitchell is shown here in this photo he sent to Renee Waring in the fall of 2008. (Edmonton Police Service )

"If you really want to make this to happen and get away with it, prepare a kill room the same way Dex does, wall to wall plastic sheeting," Twitchell replied to her in a message on Oct. 3, the same day the Crown alleges he lured and tried to kill a man who was able to escape.

Twitchell tells her to use a stun gun and a sleeper hold on the victim: "This tactic leaves no forensic evidence behind and renders your target unconscious quickly and silently."

Twitchell then tells her she should be clothed head-to-toe in disposable rain gear and "pulverize the jaw bones and remove the teeth to avoid dental ID."

The body should then be dumped "Dexter style" in a body of water with large rocks to weigh down the plastic bags, Twitchell wrote.

Twitchell's lawyer acknowledged to the jury that his client is the author of these emails.

Two days later, Twitchell writes back to Waring, this time advising her to use a "sturdy copper pipe" and to use a hunter's game-processing kit to cut up the body.

Crown prosecutors have shown the jury pictures of a metal pipe and a butchering kit that were seized by police during the investgation.

After discussing what Twitchell told her, Waring writes in her Facebook reply: "Oh well, that's what dark fantasies are ... just a fantasy."

'There's lots going on'

Waring testified she didn't hear from Twitchell the weekend Altinger went missing.

When Twitchell tells her on Oct. 14 that something has been keeping him busy and that he "crossed the line", Waring presses him for details: "You wouldn't have brought it up unless you needed someone to confide in, so spill it, Mark."

Twitchell asks her for her phone number and says he will give her a call. He tried calling once but only left a brief voice mail.

Twitchell writes Waring on Oct. 26: "There's lots going on, most of it not good."

He tells Waring in an Oct. 27 email that "there's an enormous missing person, possible homicide investigation going on centralized around a location I've been renting for film work so of course police have tossed my house and impounded my car."

He adds this was "not fun considering they won't find anything" and "not the worst case scenario".

Twitchell was arrested on Oct. 31.

The jury was told Waring sent Edmonton police all of her online communications with Twitchell several days after he was charged with first-degree murder.

With files from the CBC's Janice Johnston