Well, it could be that they want to talk to you about those documents. It could be that they are going to return them and you have sign for them ... it could be that they have proof of a crime and want to interview you ... etc. Many things COULD be going on.
If anything unlawful was going on, you may not want to go in without talking to an attorney. If you are on the up and up, then maybe you should go in. Your call.