Author Seth Rosenfeld writes about 1960's activist Richard Aoki in the San Fransisco Chronicle and explains how the FBI released information acknowledging that Aoki was considered an informant by the FBI. According to the article, Aoki was assigned the source symbol number T-2 in a released report. For those unfamiliar with FBI symbols, this means Aoki was considered a temporary source in that report. The article goes on to explain that the FBI had no comment on the matter as additional records about Aoki are the source of current litigation.
In an unrelated matter, the FBI recently lost a court fight to withhold infomant records on Ernest Withers, a photographer during the civil rights era. The FBI had released documents pursuant to a FOIA request that revealed that Withers was an FBI informant on Dr. Martin Luther King, Jr.