After consulting your attorney before answering anything, you answer their questions through your attorney. If they want your testimony live, they can subpoena

After consulting your attorney before answering anything, you answer their questions through your attorney. If they want your testimony live, they can subpoena you. I was in a real estate investing meetup at Halloween where people were sharing scary stories. The scariest was told by a guy who was, unknown to him, dealing with a corrupt mortgage broker. Two FBI agents knocked on his door and "wanted to ask some questions". He told them he would be happy to talk to them with his lawyer in their office the next morning, but he wasn't saying anything at that time. He figures that stall potentially saved him tens of thousands of dollars by not being dragged into a blanket indictment.