There seem to be just two pieces of evidence that are used to back the idea that there was some kind of drill being run on the same day as the Boston Bombing. 1) The Natural News claim about a bomb disposal drill 2) Ali Stevenson's interview For #1, they simply conflated the JFK Library with the Public Library, and then ran with it. This was full debunked here: https://www.metabunk.org/threads/1395-Debunked-Natural-News-Boston-controlled-explosion-exercise For #2, the source is: In the interview Stevenson says "at the start line this morning, they had bomb-spotters on the roof of the buildings, and they had bomb sniffing dogs coming up and down at the start line, and [my wife] said they were bomb sniffing dogs at the finish line" ... "The kept making announcements, saying to the participants, 'do not worry, it's a training exercise'. Evidently I don't believe they were having a training exercise, I think they must have known, they must have some kind of threat or suspicion called in." Firstly the thing that leaps out to me about this story is that it's just one guy. There were 23,000 runners. But nobody else is talking about this heightened security. Nobody else is commenting on people talking about a "training exercise". And with thousands of people taking video at the start, why has nobody got it on tape? It's just Stevenson's paraphrasing of what he saw and heard. Secondly, heightened security seems to be all it is. There's no "drill". Nobody said the word "drill" If anything it was simply what they said, training. And all big events have bomb sniffing dogs. It's to be expected. It's also quite expected that they will use large events as training exercises for those dogs. I myself once randomly participated in sniffer-dog training when getting off a plane - a TSA officer asked me to carry some scented object into the next room where a dog was going up and down the line. The dog correctly nosed me, and got a reward.