Before Lincoln's election, slaves who "belonged" to "owners" in the South (like Virginia) but escaped to states in the North (like Pennsylvania) were subject to the Fugitive Slave Law.
The courts allowed an owner to use "reasonable force" to detain runaways. Anyone who tried to help a detained slave escape would be subject to the scrutiny of a federal "grand inquest."
How did the laws work? The case of "Moses Honner" will make the point.
According to the U.S. Attorney for the Eastern District of Pennsylvania:
Buck was convicted at trial.