When Matthew Roberts was in grade school, the first book report he ever did was on Helter Skelter, about convicted serial killer Charles Manson. “I got a B,” Matthew, 41, tells In Touch. “I didn’t like the guy, I didn’t dislike the guy. He was just some freaky character on the news. Looking back on that, I find it odd.” It wasn’t only odd — it was foretelling. Two decades later, Matthew, who was adopted as a baby, would discover that Charles Manson was his birth father. “It was surreal,” says Matthew, who is the spitting image of the ’60s cult leader. “I didn’t want to believe it. I was frightened and angry.”

Matthew’s story is fascinating, yet complicated and disturbing. Growing up in Rockford, Ill., he didn’t know he was adopted until his sister told him in fifth grade. “I was pretty shocked,” he says. Discouraged by the high cost of adoption searches, Matthew waited until 1997 to find his birth parents. After Lutheran Social Services located his mother, Terry, in Wisconsin, Matthew wrote her and she responded right away. “She said she named me Lawrence Alexander and told me she’d tell me my last name some other time in person,” Matthew remembers. Curious and confused, he pressed his mother for more information until she finally revealed the awful truth in a series of letters.

In 1967, two years before Manson was imprisoned for the infamous Tate-LaBianca slayings in LA, Terry met the charismatic guru when he was traveling across the country in a bus with his “Family” of followers and allegedly stopped in her small town. “My grandfather chased him away and called him a ‘white-trash biker bandit,’” Matthew reveals. But hypnotized by Manson’s charm, like so many others, Terry hopped on the bus and ended up in San Francisco. While there, Matthew says, she claims she was raped by Manson and four other men during a drug-fueled orgy. Terry returned home and on March 22, 1968, Matthew was born. “It was a terrible thing that happened,” he says. “She didn’t know for sure, but she suspected Charlie was my father. She even said, ‘You look just like him.’ She sent me pictures of the other guys, who look nothing like me. It became obvious to both of us that he was the one.”