LOS ANGELES — The fun part of “The Dating Game” was the person trying to blindly select a potential date — from three people who could be heard and not seen — never knew who was going to come around the corner. They could be great-looking, a dud or somewhere in the middle. On an episode of the game show airing in 1978, the woman doing the picking made the worst possible choice. She selected Rodney Alcala, America’s most prolific serial killer.

A re-creation of that moment is part of the made-for-cable film “The Dating Game Killer,” slated to be broadcast Dec. 3 on Investigation Discovery. Guillermo Diaz (“Scandal”) takes on the role of Alcala, while Carrie Preston (“The Good Wife”) plays Carol Jensen, a mother who tirelessly seeks justice for her murdered daughter. Preston’s character is not based on a real person but is a mix of several women who lost children to the serial killer.

Diaz had to take on the disturbing role of a man with a near-genius IQ who preyed on young attractive women, luring them by claims he was a professional photographer who wanted to enter their photos in a contest. While the precise victim count remains unknown, Alcala is thought to have killed as many as 130 women and children before he was finally captured in 1980.

Playing Alcala is the latest in a long line of TV and film roles for Diaz that include “Mercy,” “Weeds” and “Girls.” None of his other acting jobs had the same effect on Diaz as taking on the playing the serial killer. Even before the movie started filming, Diaz found himself being extremely anxious and nervous about making the movie.

“Luckily enough once we started shooting, all of that went away because I could just concentrate on the work,” Diaz says. “Making the movie was kind of cathartic for me because I was able to get out all of those feelings I was having before we started.

“Positive things about the filming have stuck with me, but none of the negative.”

One of the things that made the role so difficult was despite all of the heinous things Alcala did, those who knew him described him as being very charming. Diaz had to find that middle ground of playing the character so the audience understands the insanity of what he did while also seeing how Alcala could lure so many victims to their death.

What Diaz was told was that people were drawn to Alcala and he was very good at talking with people.

“I tried to sort of focus on the humanity of this guy. All those positive qualities and then when he would go to the dark side and kill people, I could ease into that,” Diaz says. “Sadly, all these victims fell for his charms.”

Diaz briefly considered trying to arrange a meeting with Alcala, but after some very strong advice that would not be helpful, Diaz turned to research he found online, including the actual appearance by Alcala on “The Dating Game,” which he used to fill in the spaces left by the script.

“I finally decided not to go face-to-face with this guy to give him any kind of excitement about us making a movie about his life,” Diaz says. “I am sure he’s heard about it though.”

Another big help for Diaz was the hair and wardrobe he wore to play the character starting in the ’70s. The long stringy black wig Diaz had to wear to match Alcala’s look; some very uncomfortable platform shoes were the last pieces of putting together what Diaz needed for his performance.

He describes seeing himself in the mirror before he would head to set and realizing he no longer looked like himself, and that was a valuable help. Preston laughs and adds that with the constant interest in retro fashions, her wardrobe didn’t feel that different.

From the game show appearance to Alcala’s bizarre courtroom appearance acting as his own lawyer where he interrogates himself, the story has so many strange elements that it almost seems too odd to be true. That’s exactly how the story struck Preston when she read the script.

“Sometimes truth is way more terrifying than fiction. I also think that’s what makes this story so gripping,” Preston says. “The fact he was able to get away with so much before he was finally punished for it in a meaningful way.

“Then when you add in the bizarre element of him being a contestant on a game show as a convicted rapist that they didn’t catch before he went on national TV and it all becomes so interesting.”

Preston’s resume is just as long as her co-star’s with TV and film credits that include “True Blood,” “Happyish,” “Emeril” and “The Following.” She found her role in “The Dating Game Killer” forced her go to a deeper level of acting than she’s ever had to play. Her character faces not only the horror of losing a child but also the continued pain of the police not being able to do anything to get justice for her murdered child.

“The Dating Game Killer” is the latest example of the varied career Preston has had.

“I went to school for acting and it was all about transforming and becoming other people. That’s what makes me love it. I get to experience a bunch of different lives,” Preston says. “I have been fortunate I have been allowed to have those roles that are diverse.”

Diaz, whose career has also been across the board when it comes to roles, says in the beginning he was typecast as the heavy but he was convinced even stereotypical roles would show what he’s able to do. It did and he started getting more varied jobs including his latest starring role in “The Dating Game Killer.”

The movie will be followed by a premiere of “The True Story of the Dating Game Killer” at 10 p.m.

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‘THE DATING GAME KILLER’

8 p.m. Dec. 3, Investigation Discovery

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Distributed by Tribune Content Agency, LLC.

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