According to google Boston has the 20th largest police force in the US and it has 2,144 officers. When you factor in all the other police forces in Mass and the state police etc I am sure that Mass could put tens of thousands of cops on the streets all armed. Then there is the Mass national guard of course which would help out in a pinch as well.
Lucky there isn't two terrorists really then. Have they called Rambo and Arnie in yet?