Cheated by a person who sold us the land

Hi,this is pranay My father has bought land of about 170 square yards from a person 9 years ago,we paid the amount in 3 installments,he said that he will handover the original documents after the final installment(3rd),after the third installment was paid,he played a drama saying that the documents were missing,he continued this thing for few months and escaped to a new city and not accepting our calls, Later we found the former owner of the land who is a govt employee and the land was given to him by the state govt.he sold that to the person from whom we purchased,we found that this govt employee is having the original documents,second thing he again sold the land recently to another person and made gpa.we dont have any documents but a paper with the signs of both the govt employee and his wife.he sold the land to 2 persons,1.the person from who we purchased again 2.another person after a few years The person from who we bought is escaped,how to claim the land legally?