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The four-part series is based on the book of the same name written by Gary Stewart, who claims his father was the notorious murderer.
It follows his search for his birth parents, which led him to uncover information that convinced him his dad was the violent criminal who was never brought to justice.
The 'Zodiac Killer' was the pseudonym used by the person who brutally murdered at least five people - though it's claimed the number could be more than 30 - across Northern California throughout the 60s and 70s.
Evading capture, he wrote cryptic messages to the press, toying with them as he carried on killing.
But Stewart says that as soon as he saw the infamous wanted picture, he knew it was his dad.
The 57-year-old, who lives in Baton Rouge, Louisiana, said: "The wanted sketch [of the Zodiac Killer] just made my heart stop for an instant, because I had seen that face before and it looked just like my father."
Though he had always wanted to meet his birth parents, Stewart didn't meet his mother - whose husband, a police officer, had worked on the Zodiac case - until 2002.
It was then that he decided to look into his biological father: Earl Van Best Jr.
Stewart said: "He was deceased when my mother found me. But when I told her I wanted to find my father, she went to her husband's old work colleagues and her friends in the San Francisco police department and asked them. It took several months to find my father's files.
"But the information they presented to me was that there was information in that file that they were not willing to share with me - and that was pretty bad stuff."
Best Jr. was 27 when he started a relationship with Stewart's mum Judy, 13 at the time, and was later imprisoned for it.
Having delved into his father's past, it was only two years later when he watched a documentary about the Zodiac Killer that Stewart put the two together. Adding up his list of crimes and the locations, it all made sense to him.
He said: "Do we really know the genetic effect of being related to a serial killer? How does that play out in a few generations?
"[I wanted to take] that dysfunctional cycle of my father's life, and use the new beginnings from the Stewart household to give my son and grandchildren an opportunity to walk away from this and never have to be concerned with what kind of blood they have."
After finishing his own documentary, Stewart now hopes he can find some closure surrounding his dad's past.
He added: "I think my book ended [by saying] 'My father abandoned me so many years ago, maybe now I can abandon him and walk away'. And that was six years ago.
"I have not abandoned him. We spent the last year and a half filming this documentary... but this time, I'm over it.
"I'm done with it."
The Most Dangerous Animal of All airs on FX on 6 March.
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