One other point about arrests.
A lot of the reporting I’ve heard in the last few minutes focuses on whether there has been “an arrest” in the Boston Marathon bombing. Another thing we want to bear in mind is that most bombings are conspiracies, involving more than one participant. That doesn’t mean there can’t be a lone-wolf scenario, but that is not the norm.
Once law-enforcement agents make an arrest, the rules of criminal procedure require that they bring the arrestee to court for a public presentment on the charges. (There is an exception to this rule, which occurs when an arrestee waives presentment, usually because he is cooperating with the police in the hunt for other suspects. But let’s ignore that for now and stick to the usual situation.) A public presentment is designed to ensure that the arrested person understands the charges, has counsel, and knows he is under no obligation to speak to investigators (or speak any further if he has already made statements). But more important, the presentment has the effect of telling the whole world — including any coconspirators — that the police know what has happened and are mobilizing to arrest other suspects. It is a signal to coconspirators to flee, destroy evidence, and intimidate (or worse) potential witnesses.
One of the really tough calls to make in an investigation involving multiple offenders is: What is the optimal time to start making arrests so that you have the best chance of catching everyone involved? Of course, if there was more than one person involved in the Marathon bombing, it is entirely possible that at least some of them have already fled and/or begun obstructing the case against them. Still, prosecutors and agents have to try their best to catch as many offenders as possible — you’d like to have everyone “in pocket” (i.e., under surveillance and grab-able) before the first arrest is made.
This is why leaks by law-enforcement sources are so very irresponsible — in addition to being so often inaccurate. They help the bad guys a lot more than they inform the public. It is also why it is hard to have much sympathy for the media. I’ve heard some newscasters in the last hour suggesting that it is incumbent on officials to step forward and clarify what is going on because there is so much misinformation out there. But there is misinformation because the media broadcast reports based on unnamed sources whose states of knowledge vary widely and are often not what they are advertised to be.