It is perhaps the most famous self-improvement manual ever written – with supporters including billionaire Warren Buffett, music legend Johnny Cash, and former First Lady Roselynn Carter.  

But according to the authors of The Last Charles Manson Tapes: Evil Lives Beyond the Grave, America’s best-selling self-help book was also adopted as a manual by notorious cult leader and murderer Charles Manson.

Authors Andy Tillett and Dylan Howard claim that the killer first encountered Dale Carnegie’s How to Win Friends and Influence People while in prison for a parole violation in 1956.

“Manson was imprisoned in the Terminal Island facility in San Pedro, California,” writes Tillett and Howard. “The prison offered a course based on Dale Carnegie’s How to Win Friends and Influence People, which codified sales and communication techniques—techniques Manson would soon hone to manipulate others.”

A little over 10 years before he would form his notorious “Manson Family” cult, in which he declared himself a spiritual guru and persuaded his followers to carry out a frenzy of slayings to spark an apocalyptic race war, Charles Manson was little more than a petty thief – albeit one with violent tendencies – who had been in and out of correctional institutions since he was a young teen.

But it was Carnegie’s teachings that taught him the leadership and brainwashing techniques that would see Manson leave prison for the final time a decade later – and almost immediately start to recruit followers to his murderous cult, with such horrific consequences.

“Manson charmed officials into letting him enroll,” say Tillett and Howard. “He learned techniques promoted in the book such as: listening to the person you are trying to sell to and reflecting that person’s thoughts, being effusive in your gestures, as they help keep the attention of the person you are speaking and not being afraid of giving up credit for ideas.”

First published in 1936, Dale Carnegie’s book has sold over 30 million copies worldwide and is ranked by the US Library of Congress as the seventh most influential book in American history.

Originally written as a guide for budding businessmen, the manual begins with a list of “Twelve Things This Book Will Do For You." These include: “Get you out of a mental rut, give you new thoughts, new visions, new ambitions," “Increase your influence, your prestige, your ability to get things done," “Make the principles of psychology easy for you to apply in your daily contacts,” and “Help you to arouse enthusiasm among your associates."