Employee not cooperating, threatening

Sir, i am senior lecturer and incharge Head of mechanical section in a polytechnic college in telangana. A lecturer in mechanical section is troubling the section by not doing works properly. In the past one principal tried to conduct enquiry by gathering all proofs against him but he black mailed principal by filing RTI against him with fake name, by asking IT returns, previous years departmental data, etc. He has relations with police departments and threatening all the seniors who ever performs as head and sits ideally most of the times. Now Every one is afraid of taking action against him as he personally targets,and defames them. Two days back a meeting is conducted in principal chamber on his negligence behaviour, noncooperation. Infront of all he threatened me that he will approach human rights commission. Further as the college has inspection in soon dates, every staff is working hard in gathering, preparing required data...but he questions me like "the data should be prepared in past days only, why you are imposing them on me..i will go to court" infront of all he questioned me with high pitch. i have submitted two complaints against him, but the principal and others are afraid of him and not forwarding the letter to superiors as he may personally take revenge on them and blackmail them. i request you to suggest me what i can do further...and suggest me to what i can do if he goes to court, files RTIs against me, tries to blackmail me while if any enquiry gets conducted on him.