What we do know for sure is that the FBI did some questionable things to MLK Jr. The Church Report disclosed some of them. It was a report by a government oversight committee to investigate the operations of the FBI in 1976.
"The FBI collected information about Dr. King's plans and activities through an extensive surveillance program, employing nearly every intelligence-gathering technique at the Bureau's disposal."
"The FBI's formal program to discredit Dr. King with Government officials began with the distribution of a 'monograph' which the FBI realized could 'be regarded as a personal attack on Martin Luther King,' 4 and which was subsequently described by a Justice Department official as 'a personal diatribe ... a personal attack without evidentiary support.'"
"The FBI responded to Dr. King's receipt of the Nobel Peace Prize by attempting to undermine his reception by foreign heads of state and American ambassadors in the countries that be planned to visit. "
"The FBI's program to destroy Dr. King as the leader of the civil rights movement entailed attempts to discredit him with churches, universities, and the press."
"The FBI mailed Dr. King a tape recording made from its microphone coverage. According to the Chief of the FBI's Domestic Intelligence Division, the tape was intended to precipitate a separation between Dr. King and his wife in the belief that the separation would reduce Dr. King's stature. 7a The tape recording was accompanied by a note which Dr. King and his advisers interpreted as a threat to release the tape recording unless Dr. King committed suicide. The FBI also made preparations to promote someone "to assume the role of leadership of the Negro people when King has been completely discredited."
These are only the tip of the iceberg. The above quotes are only from the first page of the report.
INTELLIGENCE ACTIVITIES AND THE RIGHTS OF AMERICANS: DR. MARTIN LUTHER KING, JR., CASE STUDY