You should compute his income from past years and arrive at cash balance.
The money he deposited is not high, but you have to check overall deposits in previous years. If his income in each year is higher than exemption limit, file return for him.
You can file using 4S, that will be not an issue.
Even though receipt for the year is 6 lakhs but check his profit for past years, less drawings and check cash in hand.
If he has avoided tax liability then it is advisable to pay tax and leave a peaceful life as income tax is going to be tough in future.