If you wanted to inform something important on a criminal matter and bring the knowledge of police on that clandestine affairs, you can file a complaint under "Whistleblower policy direct to Supdt of Police and specifically request him to keep your name as secret in view of your personal security. It is a must that you have to provide prima facia evidence to substantiate your complaint. There is no prescribed format. Do not send Anonymous complaint as Govt. depts., are not supposed to act on such Anonymous complaints.