washington u.s. interior department fail provide documentation need internal probe secretary ryan zinke travel department inspector general say thursday investigation delay absent incomplete documentation several pertinent trip mary kendall department deputy inspector general say letter send week david bernhardt department deputy secretary letter publish department web site inspector general launch investigation zinke travel report emerge september use private plane own oil executives probe launch inspector general receive numerous complaints zinke travel include use three charter flight one flight take june las vegas near zinke hometown montana cost taxpayers 12,000 accord washington post report kendall letter say office receive full cooperation employees contact find documentation adherence departmental travel policies deficient without proper management oversight accountability say many authorizations vouchers require zinke travel yet complete process request documentation late dec. 11 secretary wife lolita zinke accompany government travel letter also complain department travel review process fail include proper documentation accountability interior department comment refer letter also publish web site bernhardt respond kendall speech conservative think tank heritage foundation september zinke deny inappropriate travel say travel approve career employees interior department ethics office call report use charter private flight little b.s bernhardt say letter additional document probe send inspector general office early month say department work provide available documentation zinke travel say appreciate recommendations kendall travel procedures secretary immediate office bernhardt also say zinke inherit organizational operational mess obama administration say department travel procedures obama epa administrator scott pruitt treasury secretary steve mnuchin also come scrutiny report expensive private plane use u.s. interior secretary fail provide paper travel probe inspector