I think you can start investigating Joe for an email he sent 10 years ago and that your scanning algorithm picked up from the archive only now. Maybe you're searching for matches with different keywords (the X in "war on X" changed). That email and the actions could have been lawful at the time and now, but Joe could be marked as suspicious and all sort of unpleasant things can happen to him and his friends.

If it was legal when the actions occurred, you cannot be tried. Similarly, if you committed a crime before the law was changed to allow it, then you have still broken the law.

The point here is that you can be placed on certain watchlists with no due process. No trial is required to be placed on the US no fly list or any countries terror watchlists.

Jurisdictions change.

"Ukraine’s Parliament Votes To Open Soviet-Era KGB Archives To Public" http://www.ibtimes.com/ukraines-parliament-votes-open-soviet...

In "The Internet With a Human Face", Maciej Cegłowski asks:

"What happens if Facebook goes out of business, like so many of the social networks that came before it? Or if Facebook gets acquired by a credit agency? How about if it gets acquired by Rupert Murdoch, or taken private by a hedge fund?

"What happens to all that data?"

http://idlewords.com/bt14.htm

That's just one of the problems we're facing.

At least in the US, 'ex post facto' laws are specifically forbidden by the Constitution: http://en.wikipedia.org/wiki/Ex_post_facto_law

True, but the US government doesn't even pretend to follow the Constitution anymore.

Also, the Constitution can be amended. We can't guarantee that ex post facto laws will remain unconstitutional for the duration of your lifetime.

Also, states are technically not obliged to abide by the US constitution.

The first and last paragraphs are incorrect; you may disagree that the federal government actually follows the Constitution, but that's a different issue. And while many provisions of the Constitution address only the federal government, States are still bound by it to the extent it addresses them, as it does, among other places, in the 14th Amendment.

The first paragraph is correct because I clearly meant it in figurative language, not literal language. Regardless, my point is this: the US government does not obey the US constitution.

The last paragraph is correct in context. Specifically, with regards to encryption, states are allowed to do whatever they want because the Constitution doesn't mention encryption and because of the 10th amendment, which states:

The powers not delegated to the United States by the Constitution, nor prohibited by it to the States, are reserved to the States respectively, or to the people.

The last paragraph is also correct because the ex post facto law clause of the Constitution only applies to Congress, not the states [1]

[1] https://en.wikipedia.org/wiki/Article_One_of_the_United_Stat...

The original poster is called "abritishguy". Assuming this translates to information about his location then his country according to that article (and according to it's lack of formal Constitution) has no such protection.

The US system is protected by a strong constitution. Others around the world are not so lucky.

The point is that these email records are permanent not ephemeral. And therefore they have to be viewed in a more nuanced light.

For example something does not have to be a crime to come back and bite you. This could be a job losing issue, an issue that prevents you from running for public office, or even a blackmail issue. For example (and I'm not stating my position on this issue) opposing gay marriage used to in the US be an acceptable moral stance. According to what happened to Brenden Eich this is no longer the case and emails on the topic someone sent 10 years ago might come back to hurt them today.