Your initial aim is to complete your 10+2 and any stream is ok for it and then complete your graduation too again any course is valid. Then you have to give the Combined Graduate Level Exam conducted by Staff Selection Commission, by this way you can get admitted as Sub Inspector.

There is another way by which CBI sometimes recruits its officers due to manpower crunch it is facing. It gives opportunity to police personnel with some experience under their belt to join the department and work as CBI officers.

Best wishes. Thank you.