Aaron Tang was watching and photographing the Marathon from his office when the first explosion went off. He's posted a set of photos, some taken seconds after the blast.
Meanwhile, Ethan Long reports on being inside Forum when the second bomb went off right outside:
A flash went off in the front of the restaurant. At least that's what I thought; I hadn't been the only photographer there. A second flash went off along with a huge boom.
"Get Down! There's a gun!"
I couldn't see, there was so much smoke. Glass blew by my face. A pretty heavy-set guy, I was the easiest target in the room. I had to get out. I couldn't see Alex Pearlman anywhere, and in the pandemonium, I took the first chance I could to push the table forward and jolt out the back door. Those fifteen seconds or so have become a blur. I had never felt total hysteria before. Quite a sensation, it split my brain and my body, and without much processing, I felt my body move like I was jumping from one side of a mosh pit to the other, into a friend's chest — but instead it was the side of the bar. I hadn't even thought about the bag I left, the cherished lens I'd had since I was 16, or the ATM card I had just opened a tab with. It was survival or nothing.
Public Alley 441 was no longer the devoid strip of asphalt in dire need of repairs. Instead, it became a stream of runners without bibs, and instead with infants, fathers, partners, mothers, and just about any type of person you could think of.
Tang photo used under this Creative Commons license.