Police Commissioner Edward Davis says authorities aren't certain that the explosion that occurred more than an hour later at the JFK Library was related to the other blasts, but they're treating it as if it was.
Davis says there are no injuries stemming from the third explosion. The total numbers of casualties from the other blasts isn't known.
Davis urged people to stay indoors and not congregate in large groups.
Police say they received no information before the explosions to indicate they were coming.
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