To reasearch topics such as terrorism, weapons and explosives is to put yourself at the mercy of the security measures that must be in place to prevent future attacks. This shouldn’t stop you from researching – just be able to justify why you were asking questions in the first place. And make sure your ‘alibi’ is legitmate, or you may find yourself under investigation.
My writing hasn’t taken me into such forbidden territory, but every time I venture into an area I know little about, I make sure I’ve done my homeowrk before hand. That includes doing a ‘bell check’ – does an alarm bell go off in my head when I consider writing about something? If it does, then I need to seriously look at my motives for writing such a piece.