What to do when original owner claims he never sold the property?

I purchased a property in 2008, which is a vacant land within the city limits. The property was sold by original owner (Party 1) to Party 2 who sold it to party 3 who sold to party 4. I purchased from Party 4 (so I am Party 5). I possess all the original documents including the link documents. The property as per government records is in my name . Recently the property prices increased and now Party 1 claims that this is his land and he has never sold it to Party 2 and he is fighting a forgery case in court against Party 2. As he put up notice board in the property that it belongs to him I have complained to the Police. Police verified the documents and instructed Party 1 to remove it. Party 1 removed the board but prevents me to do anything on the land bringing his lawyer who states that since the land is in a court case I cannot do anything on the land. Is this correct? How am I affected in the case between Party 1 and Party 2? What is the legal advice for me on this issue?