The intrigue surrounding this week's Democratic primary contests in South Carolina intensified Friday as campaign finance reports linked Gregory Brown, the challenger who lost to House Majority Whip Jim Clyburn, to a Republican consulting firm.

Clyburn on Thursday called for federal and state investigations after another candidate, Alvin Greene, an unemployed Army veteran who lives with his father, won the S.C. Democratic primary for the U.S. Senate.

Greene, who has an felony obscenity charge pending, "was someone's plant," Clyburn said.

Clyburn contended that Greene's campaign, and those of two other black candidates, were designed to upend the Democratic primary process in the Palmetto State. He also named Brown and Benjamin Frasier Jr., a perennial candidate who surprised observers by beating retired Air Force Reserve Col. Robert Burton in the 1st District.

As late as Thursday afternoon, the Federal Elections Commission had no public record of any of the three filing quarterly reports revealing their funding sources or campaign outlays.

But in FEC reports filed late Thursday and early Friday, Brown reported that his single largest payment was to the Stonewall Strategies firm run by Preston Grisham, a former aide to Rep. Joe Wilson, R-S.C.

Grisham was an intern for Wilson in 2003 and went on to serve as his special assistant and campaign manager.

Brown's campaign paid Stonewall Strategies $23,760 this year for "marketing" and "marketing materials," according to the FEC reports.

Brown did not respond to messages from The Washington Post, but he told the website TPM on Friday that he was unaware of the extent of Grisham's work on the other side of the aisle.

"We searched high and low, there were very few people willing to get involved. ... We searched almost two months before we came up with Stonewall Strategies," he told the site, ultimately choosing Grisham because he was willing to work for a challenger against a rock-solid incumbent like Clyburn.

Grisham, 27, called Clyburn's allegations about Brown "absolutely crazy," and said his firm would work with anyone whose policies it supported.