Criminal offenses etc.
@AC
1) you are incorrect - most serious criminal offenses require "mens rea" or a "guilty mind". That is intent. Note that can include recklessness in some circumstances plus some where a reasonable person might expect an action to lead to a more serious crime (for instance, a serious assault could be turned into a murder charge even if the intent wasn't to kill - but there still has to be an intent to do something bad). There are "strict liability" offenses where intent is not require (like many driving offenses), but with very few exceptions these do not get you a criminal record (possession of a gun being one of the few). Note that, in general, Statute Law has to explicitly state an offense is strict liability.
2) the message was sent to Paul Chambers followers as a joke - none of the recipients took it seriously, and indeed the airport that picked it up on a Twitter search considered it "non credible". If the Airport considered it to be non-credible, then how could it be considered to be a menace when clearly nobody took it that way including the potential target
3) there is an appropriate charge which quite rightly applies to those who do make a hoax bomb call. Indeed Paul Chambers was arrested on that very charge but the CPS rapidly worked out they stood not a chance in hell of a conviction (as the relevant statute specifically states intent). Instead, the CPS decided to use an old piece of legislation which was aimed at prosecuting those who were making somebody's life hell over the telephone network through malicious, threatening or obscene messages. This legislation was drafted long before the Internet, and might arguably apply to somebody intentionally sending threats via email but surely not to a joke in questionable taste which no reasonable person would understand to be menacing. How many people on Twitter have said they want to murder their boss as a joke?
4) the CPS are required to prosecute only where it is in the public interest. I fail to see how it is in the public interest to go around prosecuting random tellers of bad taste jokes.
Note that this is not a small thing for Paul Chambers. In this time of paranoia and CRB checks he will have trouble getting employment in many areas, he's already lost his post as a trainee accountant. All this for a questionable joke which would in the vast majority of cases passed everybody by and nobody would have been any the wiser. If nothing else, it is the sheet arbitrary nature of this. If you doubt it, go do some searches on Twitter for threatening words. There are plenty of people out to kill David Cameron, Gordon Brown or almost any other public figure you care to name. All, one trusts, in jest.
This could have been dealt with by warning Paul Chambers not to be so stupid in future and, if there was any real cost to the airport, seeking damages if relevant. As it is, this means that many, many people prone to the odd impetuous posting are in danger of gaining a criminal conviction.