1.) "Otherwise" means the citizens are law-abiding except when they confiscate drivers' keys which is illegal or not abiding by the law. 2.) A semicolon can sometimes be used as a "strong comma," to enhance the separation of other items in a different logical series. That is not often mentioned in grammar books, but people sometimes use it that way. Put another way, writers do not always adhere to strict grammatical conventions, but use the language and its orthography in a way that seems natural or suits them best. 3.) Both are acceptable, but it seems that "A, B, and C "is increasingly preferred.

Tricky question, for my "four penny worth" I would not start a sentence with "otherwise" and I'm not sure if the second hyphen adds anything to it either but many Americans will think it is perfect. The first hyphen is required. I'm not really sure we have a sentence here at all. 'A, B and C' and 'A, B , and C' no real difference, just different usage and how you were taught. To me (British Middle Aged) the first is correct while the second looks like Microsoft English, to others it will look fine. For me the tricky bit is the semi-colon and the colon. I generally don't use them at all. I find that you can communicate with more people if you keep your language simpler.

1) 'Otherwise law-abiding citizens' means citizens who usually follow the law. This time, they are breaking the law. 2) A semicolon indicates a pause between two main clauses. From the dictionary: "a punctuation mark (;) indicating a pause, typically between two main clauses, that is more pronounced than that indicated by a comma." 3) The last comma is called an Oxford comma and is considered necessary by most people but there is a huge argument about whether it is necessary. If you are in doubt, though, you should use it. Hope this helps. Regards, ServiceTier