Charles Manson's final words to the outside world are to be revealed in a chilling new documentary being broadcast next Sunday (3 December).

The murderous cult leader, who was serving multiple life sentences, made several phone calls from prison to filmmakers in the final year of his life.

In one, he declares: "I'm the most famous human being not only that is alive, but the most famous human being that's ever lived. And I'm not even dead yet."

He adds ominously: "What do you think is gonna happen when I die?"

In another conversation, he speaks about the slayings of pregnant actress Sharon Tate and the six other people for which he was convicted of orchestrating.

"I never ordered nobody to do anything," a remorseless Manson says. "They were always free to leave."

The teaser for the documentary, called Charles Manson: The Final Words, and obtained by TMZ, also gives a glimpse of how Manson sees himself amid his position as one of America's most notorious killers.

He explains: "I've been deep in thought in solitary confinement for almost 40 years thinking, 'What the hell does all this mean? How does that fit? Where does that work?'

"And the stuff that I've come up with man it's just unbelievable."

The documentary was initially scheduled to be shown in 2018 but cable network REELZ decided to bring the airing forward following the 83-year-old's death on Sunday (19 November).

It features phone conversations with Manson – the most recent in July – from Corcoran State Prison, and presents a fresh theory behind why the murders took place.

A petty criminal who had been in and out of jail since childhood, Manson's killing spree came after he reinvented himself during the so-called Summer of Love as a long-haired, Christ-like guru spouting Bible verses and Beatles lyrics.

After attracting a few dozen followers from San Francisco's Haight-Ashbury district – many of them young women and runaways – he took them to an old ranch on the edge of Los Angeles that he transformed into a commune of sex, drugs and music.

On 9 and 10 August, 1969, he was said to have sent some of his devotees out on a murderous mission to two of Los Angeles' wealthiest neighborhoods, where they killed pregnant actress Tate, several of her society friends and others. Most of the victims, including coffee heiress Abigail Folger, were stabbed.

Tate's husband, Oscar-winning director Roman Polanski, was out of the country at the time.

Prosecutors would later say that Manson had hoped the killings would touch off a race war. He had apparently gotten the idea from a twisted reading of the hard-rocking Beatles song "Helter Skelter."

Despite the overwhelming evidence, Manson maintained his innocence.

He and three female followers, Susan Atkins, Patricia Krenwinkel and Leslie Van Houten, were convicted of the murders.

They all appeared sporadically at parole hearings where their bids for freedom were repeatedly rejected.

At a 2012 parole hearing Manson boycotted, he was quoted as telling a prison psychiatrist: "I'm special. I'm not like the average inmate. ... I have put five people in the grave. I am a very dangerous man."

The parole board decided he should stay behind bars for at least 15 more years.