If you want overall prevention, the activities have to be reported to your high authority as Whistleblower and through a friend or relative to avoid harassment from superiors and colleagues.
If you are aware of specific instances then to Anti-corruption Bureau for State and CVC in case of Central Government.
In the case of the state, if the victim is prepared to co-operate the best remedy is the Red handed trap, and ACB generally agrees for this specific case, as establishing corruption is very difficult in other ways, as victims may deny or do not want to involve.
In spite of the cases, one can not find even 25% cases where the courts punish the errant/corrupt employee and most of the times it is only at the lower cadre that was punished.
Contact a local voluntary organisation and provide feed to them and never involve yourself directly.