Well someone appears to have been afraid of them though.
Perhaps a deranged patient who went to one or more of these for treatment, was not helped and is dying of a disease these treatments claim to halt or cure. The murdering of doctors giving similar treatment regimens would be seen by the deranged mind as ‘protecting future patients form the quackery’. Investigators are no doubt checking patient lists and relatives of patients who have recently died under one or more of these doctors’ care.