The Dexter Copycat Killer Explored
Oct 23, 2026
Life Imitates Art is a tale as old as time
that sometimes has malevolent consequences,
namely the phenomenon of copycat killers,
individuals who base their crimes on acts
of violence already committed by another person, real or fictional.
Today on Scream to Screen,
we analyze the real-life tragedy behind Mark Andrew Twitchell.
Dexter Morgan is the sociopathic
protagonist of the Darling Dexter book series,
written by Jeff Lindsay, as well as the television
and series Dexter, starring Michael C. Hall.
In both the novels and TV series,
Dexter is a forensic blood splatter analyst
who works for the fictitious Miami Metro Police Department
and holds a dark secret.
In his spare time, he is a vigilante serial killer
who targets other murderers who have evaded the justice system.
He follows a code of ethics taught to him in childhood
by his adopted father, Harry, which is referred
to as the Code of Harry, or simply just The Code,
and hinges on two principles.
Dexter can only kill people after finding
conclusive evidence that they are guilty of murder,
and he must not get caught.
For the vast majority of his murders,
Dexter incapacitates his victims by injecting them
with an anesthetic, rendering them temporarily unconscious,
where he takes them to his private killing site.
When the victims awaken, they are
bound to a metal table with plastic wrap
before Dexter kills them using various methods.
In the books, he's known to torture his victims
with various sharp knives, but in the show,
prefers to use more immediate methods of delivery
to the great beyond.
Dexter ultimately stows his victims
in black heavy-duty trash bags and disposes of the evidence
by dropping the blood-soaked bags offshore to be dispersed
into the Gulf Stream.
Mark Andrew Twitchell was a Canadian filmmaker
convicted of first-degree murder of John Johnny Brian Altinger
in 2011.
His trial attracted particular media attention
as it became apparent that the murderer idolized Dexter
Morgan.
Wanting to reenact the life of Dexter,
Twitchell had adopted his persona on Facebook
and made a movie that was similar to how
the sociopathic antihero operates on the Showtime series.
After writing a script for a Dexter fan film,
Twitchell began posing as women online,
interested in having an affair with married men.
In October 2008, Johnny Altinger unknowingly
interacted with Twitchell on the dating website Plenty of Fish.
On October 10, Altinger informed his friends
of his plans to meet a woman he had been chatting with online,
only to discover much too late that Twitchell
had been catfishing him in order to lure him
into a setup in his garage, complete with Dexter's
infamous metal table.
Twitchell then proceeded to take Altinger's life
and then attempted to get rid of the remains
via a nearby storm sewer.
Following his disappearance, Altinger's friends
grew suspicious and concerned after receiving emails
in which Altinger claimed that his date had taken him
on an extended vacation to Costa Rica.
This was an immediate red flag, as the email did not
read in Altinger's usual tone, and his friends
all knew he doesn't like hot weather.
After his employer received a cryptic email detailing
his resignation, Johnny's friends
broke into his condo, where they found his passport,
dirty dishes, and no indication that he had packed for a trip.
They reported their concerns to the Edmonton Police Service,
and a homicide investigation was soon launched.
Although Twitchell was not initially a suspect,
he related an improbable account to police
of having met Altinger before his trip to Costa Rica.
According to Twitchell, Altinger sold his car to him
for $40, claiming to not need it anymore now that he'd
be on holiday for a while.
Not believing his story, officers
searched Twitchell's home and found
a plethora of science fiction memorabilia and film posters.
They also found books about forensic science,
serial killers, and a guide to Costa Rica,
along with a pile of blank postcards and a black hockey
mask with gold stripes, which appeared to have blood on it.
Once authorities impounded Twitchell's laptop and car,
they uncovered a military knife stained
with Altinger's blood and blood soaked carpet
in the vehicle's trunk.
Investigators also found dozens of post-it notes
with cryptic messages scrawled on them
like kill room, clean sweep.
Twitchell was arrested on October 31, 2008,
and charged with the first degree murder of Johnny
Altinger the same day.
The key piece of evidence presented by the Crown
at Twitchell's murder trial was a document entitled
SK Confessions, or Serial Killer Confessions.
The document which had been recovered
from Twitchell's laptop despite having been deleted
began with the passage, 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.
SK Confessions presented an account of its narrator's
planning, failed first attempt, and successful second attempt
to lure a man into his garage and murder him using
fake online dating profiles as bait.
It went on to describe the process
of dismembering the body and attempts
to dispose of the remains.
The document read that the killer wanted
to target married men who were cheating on their spouses,
but he feared that they'd be missed.
Instead, he decided to focus his killing
on middle-aged single men.
It outlined what the killer would wear when he murdered
the men, a black hockey mask painted with gold stripes
and a black hooded jumper, and told
of how he would murder his victims in a kill
room on a metal table,
just like Dexter.
The Journal also wrote about another target
who had managed to escape from the killer a week
before the second murder.
The document said that the man arrived at the garage
and was attacked with a stun gun but didn't go down.
Instead, he fought his attacker and got away in his car.
Police didn't believe Johnny was the first person
to visit the garage and held a press conference announcing
Twitchell's arrest, presenting the black and gold hockey mask
and urging other victims to come forward.
Two days later, Giles Tetreault
contacted authorities, revealing he was the first man
to be attacked in the garage a week later
before Johnny Altinger's death.
He was embarrassed to report his assault
as he was a married man, but he knew
that he had to come forward after Johnny's death was
linked to the mask.
Tetreault testified that he was lured using the website Plenty
of Fish, expecting a date with a young woman named Sheena,
only to be attacked by a man in a hockey mask with a stun
baton when he arrived at the garage in Edmonton
rented by Twitchell.
After a violent struggle, Tetreault escaped,
but did not report the attack to police.
Giles Tetreault's testimony earned him the nickname,
The One Who Got Away, by several media outlets
and went on to write a book of the same title,
detailing his account and close call with Mark Twitchell.
During the trial, Twitchell's strong interest in the Dexter
series kept coming up, and his personal identification
with the lead character, Dexter Morgan,
prompted several media outlets to refer to him
as the Dexter Killer.
On the stand, Twitchell admitted to killing Altinger
and authoring the document, citing self-defense.
He claimed the attacks were part of a PR stunt meant
to cause a buzz around the new movie
and that all the victims were supposed to escape.
But Johnny had fought back, resulting in Twitchell
accidentally killing him.
He went on to describe the document
as fiction based on fact, as if he had planned Altinger's death
deliberately in order to craft a compelling story.
Unsurprisingly, the jury didn't buy this fabricated account.
And after just five hours of deliberation,
Mark Twitchell was found guilty on first degree murder
and sentenced to life in prison without the possibility
of parole for 25 years.
In December 2021, Michael C. Hall
stated in an interview on the Canadian radio show Q
that he did not think Dexter supported the lifestyle
of serial killers.
When the subject of Twitchell came up,
the actor became horrified that his breakout role could have
something to do with someone's murder.
Marc-Andrew Twitchell was not the only fan
to take his infatuation with Dexter Morgan to macabre heights.
In 2009, 17-year-old Rising Sun resident Andrew Connelly,
who claimed to identify with the murderous vigilante,
strangled his 10-year-old brother to death,
citing his love for the Showtime series as an inspiration.
In an affidavit filed on Ohio County Court,
Connelly told police that he watches a show called Dexter
on Showtime about a serial killer,
and I feel just like him.
Even more sinister, after killing his brother,
Connelly put a plastic bag over the young boy's head,
mimicking a practice that Dexter ritually commits
to dispose of his victims.
Conley pleaded guilty to the murder
of his young brother, Connor, on Ohio Circuit Court in 2010.
The now 29-year-old is currently serving a life sentence
without parole with the Indiana Department of Corrections.
Copycat killings are murders committed
in a way that is already established by previous murder
committed by someone else.
Some credit the year 1912 with the birth
of this class of killer, with intense media
coverage of the Jack the Ripper murders
spawning a multitude of similar crimes
and coining the term copycat effect.
Modern criminologists have long been
aware of the potential for media exposure
to lead to copycat killings.
As the media has grown, other forms of entertainment,
especially movies, television series, and video games,
have come under fire for allegedly
leading to copycats based crimes on what they see on the screen.
Outside of Dexter, Jack the Ripper
may be the most notorious killer to inspire protégés,
spawning dozens of copycat killers
over the last century, including Derrick Brown, who
murdered two women that he picked up
from the same location in East London,
where the Ripper carried out his murders over 120 years prior.
Other famous copycats include Eddie Setta,
who echoed the Zodiac Killer in the late 1980s,
and Benjamin Derris and Sarah Edmondson, a teenage couple who
went on a killing spree the day after watching
the film Natural Born Killers while under the influence
of LSD.
So there you have it.
The story of Dexter Morgan and the not one but two copycat
killers who became influenced by his fictitious work,
along with some other notable copycats,

