To put it short, he was a guy who led federal officers on a chase through the desert. They didn’t know who he was, but he was stealing from travelers passing through. It wasn’t far from some US government facilities, and this being not long after 9/11, they’re super worried he’s a terrorist.
Spoiler: he was a Canadian who started growing weed to help his wife’s medical issues. He apparently made some primo bud and started selling it. Naturally, he got caught and was thrown in jail. When he got out, he moved out to the desert and tried to survive on his own.
Jail changed him. He became more paranoid and detached from his family, friends, and society. He wasn’t the least bit dangerous until they threw him in prison.