Why are detectives waiting for Harper when he arrives home from checking on Erin? How does Harper react?

When Harper returns from checking on Erin in Jackson, Michael Mayeux and Detective Jim Overstreet from the Jackson Police Department are waiting for him. They are going to place him under arrest for obstruction of justice and harboring a federal fugitive - Miles. Harper goes with them without struggle, but drops his father-in-law's name and is released within a short period of time.