Theres a story that The Hump was so paranoid in his last days that he used to change his apartment keys every few days in case the FBI somehow copied them.

Also that he even wanted to order a beating or a hit in worst case on journalist Sandy Smith for calling him stupid and that he did a foolish move to evade subpoena in 1965.

I also belive that no way the mob would've killed him.He was a legend among gangsters but the thing is some of these "legends" die in a awkward situations and brings the belief of something suspicious,something like the case's of Luciano or Longie Zwillman.