Vincent T. Bugliosi, "who...

...successfully prosecuted the cult leader Charles Manson and several acolytes for the savage murders of the actress Sharon Tate and six other people in August 1969, then became a best-selling writer of true-crime books, died on Saturday in Los Angeles. He was 80."

From his obit in the Times (my emphasis):

Mr. Bugliosi’s account of the crimes, “Helter Skelter,” was written with Curt Gentry, who died in 2014. Originally published in 1974, it has sold over seven million copies and is the best-selling true-crime book ever. It won an Edgar Award from the Mystery Writers of America as the best true-crime book of the year.

I read Helter Skelter back in the late 1970s, I think. I'm not much for that sort of genre but read it at the urging of my brother. As you open the book the first page reads: "The story in which you are about to read will scare the hell out of you."

Truer words were never written. Why? Because it really happened.

P. S. Don't read it in your house alone at night.