I realized some of the time references in my post below may have been confusing, so thought I’d clarify.
I crossed the finish line at 2:22pm real time, and have a text from my sister from 2:40pm that I got as we were leaving the finish line area. The explosions went off at 2:51.
My race time was 3:57, but that was by a different clock than the one that reads 4:09 in all the videos and photos. There are so many runners that they stagger their starts in three different waves. Basically, the first wave was for the elite runners, second wave was for normal runners who had entered with a fast enough qualifying time (the wave my dad and I were in), and third wave was for runners who had entered by raising money for charity.
Which also means that most of the runners who were crossing the finish line when the explosions went off were running for a cause, and the spectators in the stands were the ones there to support them. The fact that most of those injured were spectators who were probably there cheering on friends and family who were running for charity, for which this was a once in a lifetime event, somehow seems particularly cruel.