The most notorious American killings of the 20th century were in part put into motion by a little-known Californian motorbike gang called the Straight Satans – that’s according to a new book by authors Dylan Howard and Andy Tillett.

In July and August 1969 Charles Manson’s “Family” cult brutally murdered nine men and women including the seven infamous Tate/LaBianca slayings, and the catalyst for their orgy of killing was the Straight Satans biker gang.

Writing in the book “The Last Charles Manson Tapes: Evil Lives Beyond the Grave,” Howard and Tillett explain how four months before the March 1969 murders, Danny DeCarlo -- treasurer of the Straight Satans -- fell into Manson’s orbit.

He had turned up at the Spahn Ranch where the Family were staying, looking for a place to repair his motorcycle. The cult leader immediately saw in DeCarlo an opportunity to add some muscle – and firepower – to his predominantly female following.

“Manson had hoped DeCarlo would convince the rest of the Straight Satans to join him at the ranch,” write Howard and Tillett, “so he could use them as a security force to scare off ranch visitors who got overly friendly with his girls, or obnoxious with Family members.” Furthermore, “He and his father had sold guns, earning him a place as chief of the Manson Family armory.”

Things soured after a drug deal brokered by the Family between the Straight Satans and a man named Gary Hinman went wrong. According to the later testimony of Family member Bobby Beausoleil, Hinman had sold them a dud batch of mescaline – and the bikers held Manson’s cult responsible.

“Unfortunately, the drugs were either tainted with strychnine or ineffective, according to whoever was telling the story,” explain the authors. “At any rate, the Straight Satans were understandably not pleased and wanted their money back. Manson was not pleased, either; the money from the drug sale was supposed to help support the Family." 

“On July 25, 1969, at Manson’s urging, Beausoleil, [and fellow Family members] Susan Atkins, and Mary Brunner went to Hinman’s home.”

Hinman refused to give Beausoleil any money – and so, on Manson’s orders, he, Atkins, and Brunner brutally stabbed and then suffocated him, though only after torturing him for three full days.

It was the beginning of what Manson would dub “Helter Skelter,” his bloody wave of terror that he hoped would spark a race war.