Because there's nothing a child wants more than to reconnect with his Family.
So Roberts initially corresponded with his biological mother through letters, and eventually discovered that she had more than a few cats running around in her skull. But the real shock came when he was finally able to chip a big enough hole through her insane ramblings to get some information about the identity of his father.
She told him that his real dad was one of four men whom she'd had sex with at an orgy in 1967, which is already a less-than-romantic story. But when she saw a photograph of Roberts, she knew instantly which one it was: an aspiring musician named Charles Manson. You may have heard of him.
"Oh, he's a musician too?"
Roberts was horrified, but for some insane reason, he decided that blood was thicker than water and started writing letters to Manson in prison. Manson, who once answered an interview question with "wolf kabob roth vanich gefrannis boojapoochaboojujube," was understandably difficult to talk to. But Roberts got enough information from history's most notorious murderer to suggest that what his mom had told him was true.