The same way they would determine a bank robbery, I guess, suspicious-acting people. It looks like they were meant to intimidate the fraudulant voters. As the bible says, law-abiding people have no reason to fear His sanctioned powers that be, but His sanctioned powers that be are a terror to the law-breaking. No one was shot for voting McClellan so your theory is ridiculous, it's clear they were after the arsonists.
All Democrats and anyone not overtly loyal to the evil race-hustling pimp Lincoln, rapist of the Constitution, was considered "suspicious-acting."
[#3Fan] As the bible says, law-abiding people have no reason to fear His sanctioned powers that be, but His sanctioned powers that be are a terror to the law-breaking.
In #3World, He appeared in the form of Spoons Butler. No wonder you are such a mess, #3. You worship an image of Spoons Butler.