Reid aide Jose Parra first made the claims in an interview on Los Angeles' KTLK radio, defending his boss' decision to trumpet the tax charge last week on the Senate floor and explaining a bit about the source.
"This person is an investor in Bain Capital, a Republican also, and somebody ... who has been dealing with Romney's company for a long, long time and he has direct knowledge on this," Parra said.
Parra's statement comes after Romney, in an interview with Fox News, challenged Reid to identify his source.
However, after some media attention on Parra's radio interview, Parra issued a statement taking those remarks back.
"I do not know the party affiliation of the source, how long he invested with Bain, or his relationship to Romney beyond the fact that he was an investor with Bain Capital, as Senator Reid has previously stated," he said.
Asked Friday about the mix-up, a Reid aide told FoxNews.com the senator "does not have any plans to reveal further information about the identity of his source."