LBJ appeared to sign off on the order and it appears Hoover was apprised and made his agents available to the CIA to get it done. From latest docs released while Trump was in office at National Archives.

Martin Luther King, Jr. was a communist. You will never see that printed in an Establishment textbook, heralded in the controlled press, or mentioned in one of the numerous whitewashed MLK documentaries on the History Channel. Yet, despite officialdom’s deliberate cover-up of King’s communist activities and affiliations, the truth is that this so-called hero was actually a communist agent who worked to subvert our Republic.

https://theamericancitadel.com/2018/01/15/mlk-communist-revolutionary-plagiarizer-degenerate/

https://kinginstitute.stanford.edu/encyclopedia/levison-stanley-david

In 1956 Stanley Levison, a Jewish attorney from New York, began raising funds to support the Montgomery bus boycott and became acquainted with Martin Luther King, Jr. The two men developed a close relationship in which Levison not only advised King, but also aided him with the day-to-day administrative demands of the movement. In 1963, the Federal Bureau of Investigation (FBI) used King’s relationship with Levison, who they believed to be a Communist functionary, to justify surveillance of King.