Though the time frames may seem different (two months vs. two minutes) they really are not. Not with anthrax, botulism, suitcase nukes, turbo small pox, etc. hanging over our heads. At this point the 'invasion' remains very much in progress and defensive measures, whatever they may be, may be warranted.
At this stage we may have to wait to determine if the use of 'deadly force' was justified. Still too early IMO.