ignorance of law is not an excuse.
u should have got the all title clear certificate, and should have done the mutation entry check. also, all the recent chain of owners should be checked in 7-12 utara or 6-12 utara list.
u should have got the property card from the tahsildar office.
or u could have checked the due diligence of the property for the past 30 yrs.
should have gone to the local municipality ward office to check the property tax on the property and all this would have given u the hint that the property has been involved in a case.