NEW DELHI, Feb 15 — CBI files case against ex-chief engineer a former Chief Engineer of Arunachal Pradesh Government and seven firms for allegedly conspiring and causing a loss of crores of rupees to the State Government. The CBI, after filing an FIR, also raided the residential premises of the former Chief Engineer in Chandigarh and official premises of these companies and seized some documents, agency sources said here. According to the FIR filed by the CBI, the former Chief Engineer Darshan Singh had allegedly abused his official position and conspired with Hydro Power Equipment, Johrat, M R Power Project, Guwahati, Horizon Hi-tech, Kolkata, M C Enterprises, Itanagar and three other firms, and caused a loss of crores of rupees to the State Government exchequer. The CBI alleged that after entering into criminal conspiracy, the accused officials had shown favours to these companies in the matter of awarding of contract for supplying of Hydel eqipment.