In 1995 James Petty was working as a talk-radio host in Gulfport, Miss., when his African-American boss showed him a copy of a postcard sold widely during the '30s. Under a photo of a lynch mob arrayed around the charred remains of a black man was a handwritten warning: "This is what's going to happen to you." Petty, 44, is white, but the card shook him so deeply that he set out on a mission—to found the nation's first museum of slavery and segregation. "I want people to see," he says, "what Americans are capable of doing to Americans."

To that end, he's gathered the largest collection of slavery-related artifacts in the U.S.—15,000 items, from whips and auction posters to a slave's button bearing the master's name. Petty and his wife, Mary Anne, 42, have poured thousands of dollars into the hoard, which they keep in bank vaults and secret locations and show at schools near their Gulfport home. "Oh, man, is it moving," says Elder Rick August, 43, minister of the Greater Grace Apostolic Assembly, who invited the couple to give a presentation.

Southern California-born Petty paid little attention to racism until, at 23, he grew close to a black neighbor. Working as a government security expert, he devoured books on African-American history and started collecting artifacts. In 1991, Petty hired on at Stennis Space Center in Gulfport, where he met and wed Mary Anne, a casino dealer. A gambling expert, he landed a radio show on the topic and later hosted a syndicated series, Las Vegas After Dark. But in 2001 the Pettys quit their jobs, sold their other antiques and now seek backers for a $45 million museum. "You see a branding iron in a book, it's just a drawing," says Petty. "You hold it in your hand, it strikes home."

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