Boston Marathon bombings
Police still haven’t apprehended a suspect related to the bombings (that we know of). I’ve heard several people speculate today that the culprit will turn out to be Islamist extremists, but I could see it just as easily being a homegrown crazy. Apparently the bombs were made out of materials that are very easy to acquire and put together into an explosive device.
The fact that there were 4 might mean it’s more likely to be an organized terror group, instead of an individual, but this wasn’t anything high-tech.