Final answer:
Ex post facto laws cannot be applied and are laws that were passed after the alleged crime, which Option A correctly states. These laws are banned by the Constitution and cannot retroactively criminalize an act or increase punishments for crimes committed before the laws were enacted.
Step-by-step explanation:
No level of government may try a person under an ex post facto law, meaning a law that was passed after the alleged crime. The correct answer to the question is Option A: After the alleged crime. An ex post facto law is one that has a retroactive effect, which can be used to punish individuals for acts that were not considered criminal at the time they were committed or to increase the severity of punishment after the fact. Such laws are prohibited by the Constitution to protect individuals from being penalized by laws that were not in place when their actions were taken.
Both the federal and state governments are restricted from enacting ex post facto laws. This legal principle ensures that laws are fair, just, and not arbitrarily applied retroactively.