I can verify that there were several JWs running the marathon yesterday. Several were within a mile of the finish line when the bombs went off. One of them had crossed the finish line less than 30 seconds after the first bomb went off so was very close. They are all safe and sound.
I'd post more, but don't want to "out" myself....
As of JWs being on the scene for "support and comfort" none of the Boston-based JWs that I know have related any such experiences. The media did mention that several people were walking up and down the marathon route sharing Bible verses for comfort.....but they turned out be Lutherans!!!