The theories on Who Did It, because it's time for wild speculation before the facts are in!
I'll LJ cut it, though, just so nobody has to see it who doesn't want to.
Okay, there are three major possibilities for who was behind the Boston Marathon bombings. Islamofascist terrorists, domestic anti-government militia terrorists, or some lone crazy person.
And, of course, it might be none of these.
But let's look at them.
First: Islamist terrorism. What are the arguments in favor? The Boston Marathon is an international event with high visibility. It's an American tradition, it's a soft-target crowd, it is symbolic. It's a good symbolic strike against America.
Second: domestic militia terrorism. Arguments in favor? Largely the date: Patriots' Day is a celebration of Lexington and Concord -- it's the Monday of the week in which April 19th occurs. April 19th is an important day to anti-government militia terrorist organizations: it's not only "The Shot Heard 'Round The World", starting the American revolutionary war, which they identify with, but it's also the day of the Waco compound raid, and of the Oklahoma City bombing. An additional date-based argument is that April 15th is Tax Day.
Third: individual crazy person. Arguments in favor? If the devices were black-powder explosives loaded with ball bearings, which is what I heard Somewhere From Somebody Probably On The Internet (so you KNOW it's accurate), that's a pretty easy bomb to make. This wasn't an attack that needed any great deal of planning, preparation, or co-ordination, and it is exactly the kind of high-visibility thing that crazy people who want to hurt people seem to like to do.
I don't have any actual reason to prefer one of these theories to another, but I feel that domestic militia terrorism is the most likely, because it best fits my preexisting confirmation bias.
However, I wouldn't be too surprised if it turned out to be a two sixteen-year-old boys from the suburbs. Because from Leopold and Loeb on forwards, if you're looking at a murder or murders with absolutely no rhyme or reason behind it, you're usually looking at a teenage boy or two. There are exceptions (Brenda Ann Spenser, who didn't like Mondays), but that's the way to bet.
And, of course, Islamist terrorism is on the table, although, to me, it feels like the least likely of the three possibilities, probably because of my aforementioned confirmation bias.
But I think we should also consider alternative theories.
The first one I mention is one that I wrote as a comment to Andrew Greene on Facebook -- the possibility that this was just someone who forgot that their explosives were armed when they threw them out in the trash cans. My mother doesn't believe that one, though, because they were in two different places, and she figures that if SHE was cleaning out her backpack and throwing out explosives, she'd just have dumped them BOTH in the SAME trash can.
So I'm going on to my second theory, which is that it was Wayne LaPierre, who wants to demonstrate that taking away people's guns won't make anyone safer, since people can kill people in other ways.
The third theory is, of course, that it was The Amuurikan Gummint, who did this in order to take people's guns away. This theory is incompatible with my Wayne LaPierre theory, of course.
Any other theories anyone wants to float out there? I haven't figured out how to tie in the Illuminati or the lizard people who live inside the hollow earth.
Edited to add: At the advice of folks in comments, I've changed the word "Islamofascist" to "Islamist". Also, the description of the explosive devices as built on a plan that's common in Afghanistan and Pakistan increases the odds of it being Islamist, and decreases the odds of it being some kid from the suburbs, although all those options are still on the table.