Rocker Tom Petty is still keen to uncover a family mystery because he thinks his grandfather was on the run after killing a man.

The AMERICAN GIRL singer claims a huge part of his family's past remains a puzzle because his older relatives refuse to talk about his grandfather and why he moved his kin from Georgia to Florida.

Speaking candidly in his first official biography, CONVERSATIONS WITH TOM PETTY, the rocker tells writer PAUL ZOLLO (corr), "My father's mother was a full-blooded Cherokee Indian... My grandfather was a white guy... (It was) not popular, to mix the races. They didn't dig it at all.

"He was stopped on a road by several guys. Some kind of violent situation came down about him being with an Indian. And somebody got insulted, and my grandfather ended up killing a guy. That's what my father told me."

Petty recalls his father only enlightened him about the family's controversial past a decade ago and he has since discovered more about his grandfather's story.

The rocker admits the story seems to fit his grandfather's mysterious image.

He adds, "I only met my grandfather a few times. He wasn't around much. He wore a big hat. He was a very mysterious guy."