Where to find evasion of income tax information

Sir, kindly advice on the following. One of my cousin is working in a hospital was getting very meager amount of salary 4K for the last three years whereas a casual labour in kerala gets Rs 1,200/- + perks daily. Contrary to the actual payments made by the hospital to its employees, the hospital filed its income tax return showing the salaries of employees at par with the payment of Govt employees. More precisely, the hospital was actually paying 4k to an employee but in the ITR it showed as Rs 40K, which made them to evade huge tax evasion. How it can be bring in notice of the authority to take appropriate action? Can income tax department help in this matter? Will an RTI application to IT department will work out? what should seek and where to approach? What are the evidences required? Where can I get the data of income tax filed in the name of salary of employees and the actual payments made to the employees?