How do I complain about black money?

Hello one of my friend's father gave him money and asked to deposit it to his bank account. The amount was not deposited at a time but in a period of 1-2 years it was in total around 45-50 lacs. The son was not aware of the source but as father gave him the amount he just did what he asked to do considering our Indian society, we do not ask such questions to our parents. That time my friend was adult (25+ years), the amount was also then withdrawn with cheques which were signed of course by my friend. The amount was used to purchase a plot which was under his father's name. Now the issue is, his father is going through enquiry and corruption case, his son was also called for the enquiry and his bank account is seized. What legal actions can be taken against the son and what can be done to get out of it as he was not really aware of anything.