That photo of the Rev. Dr. Martin Luther King, Jr. riding one of the first desegregated buses in Montgomery, Ala.? He took it. The well-known image of black sanitation workers carrying I Am a Man" signs in Memphis? His. He was there in Room 306 of the Lorraine Hotel, Dr. King's room, on the night he was assassinated. But now an unsettling asterisk must be added to the legacy of Ernest C. Withers, one of the most celebrated photographers of the civil rights era: He was a paid F.B.I. informer. On [September 12], The Commercial Appeal in Memphis published the results of a two-year investigation that showed Mr. Withers, who died in 2007 at age 85, had collaborated closely with two F.B.I. agents in the 1960s to keep tabs on the civil rights movement. From at least 1968 to 1970, Mr. Withers, who was black, provided photographs, biographical information and scheduling details to two F.B.I. agents in the bureau's Memphis domestic surveillance program, Howell Lowe and William H. Lawrence, according to numerous reports summarizing their meetings. The reports were obtained by the newspaper under the Freedom of Information Act and posted on its Web site. While he was growing close to top civil rights leaders, Mr. Withers was also meeting regularly with the F.B.I. agents, disclosing details about plans for marches and political beliefs of the leaders, even personal information like the leaders' car tag numbers.