It has been common for the government to have public executions without trial when an american citizen is known to say "bad things"
Saddam Hussein did a little more than just saying "bad things"
I wasn't aware that he was an american citizen.
Plus we didn't off him when he was murdering Kurds and other "undesirables", or when he started a revanchist war against Iran that resulted in several hundred thousand, possibly a million, casualties. He only got in the doghouse for seizing Kuwait, threatening the carefully engineered balance-of-powerlessness established in the middle east by the the allies after WWI.