1. Why wasn't he treated as an enemy combatant? This is by far the least sensible question asked in the hours since Tsarnaev was caught. The simple answer is: because he couldn't have been. The Constitution, and federal statutory law, prohibit the government from treating as an "enemy combatant" a U.S. citizen accused of committing crimes on U.S. soil. End of story. You could argue, as some have, that Tsarnaev was treated as a ''combatant" because he was not immediately read his Miranda rights. But the "public safety" exception to that constitutional rule is unrelated to the government's designations of "combatants." You or I could theoretically be subject to the Miranda exception (which would be scary); we could not be considered "enemy combatants" and thrown into Gitmo (which would be even scarier).
2. What exactly happened today in that hospital room? Tsarnaev was not arraigned. He was not asked to enter a plea. He was merely checked into the federal system with his initial appearance and was advised of the charges against him. The presence of the bedside magistrate tells us that the feds want to push forward quickly here, to get the case into the federal civilian system, both to neutralize the nonsense offered up by Sen. Lindsey Graham and company and to put pressure on the defense. Soon there will be a federal trial judge assigned to the case. Soon it will look much like the hundreds of other bombing cases handled by the federal courts since the beginning of the Republic.
3. What does the federal complaint tell us? Not much that we don't already know. It's important to remember that this document is just an initial expression of the government's case against Tsarnaev. It is a document designed to keep the suspect in custody; to ensure that he is not freed by a judge or permitted out on bail or bond pending a more formal indictment. The substance of the charges are pretty basic and unsurprising to those following the case. When you use a "weapon of mass destruction" (a bomb) to blow up people, and you do blow up people, it's a federal crime. We'll likely know more when we see the grand jury's indictment and that won't come for weeks.
4. Why no murder charges in the federal complaint? Another easy one. Murder is typically a state crime and federal murder charges occur only when a murder victim is a federal employee or otherwise related to the federal government. Because the 1995 Oklahoma City bombing ripped apart a federal building, it had many such victims, which is why it included federal murder charges. By contrast, the Marathon bombing fatalities were all civilians. What will happen now is that Massachusetts authorities will wait to see how the federal case unfolds before deciding whether to prosecute Tsarnaev on state charges. Such a case would occur after the federal case. The authorities, in other words, will have two bites at this apple.