MLK and secret FBI documents?

Many white supremacy groups claim that Martin Luther King, Jr. was involved with a white prostitute on the night before his assassination. They will also claim the FBI has files which have been locked away for years. They also claim the Dr. King plagarized his doctoral dissertation. Are any of these claims true? Did J. Edgar Hoover really claim “A tomcat has more morals than Martin Luther King?” Or, are these just racist claims made up by white supremacy groups?

I’m not linking to the websites as it is a violation of the terms of the SDMB to link to hate groups.

Here’s part of the answer, from an authoritative source:

Was Martin Luther King Jr. a plagiarist?