As to it looking like a terrorist attack to the rest of the world: it was.
Protocols for Half Mast
Thank you, Quazi!
CNN is reporting that sources tell them that one of the bombs was hidden inside of a metal pressure cooker concealed in a backpack.
I assume that when (and if) a dog encounters pepper, it signals that to its' handler, and another dog is brought in, as you suggested. And it's probably a huge "tell" that something is being hidden nearby