If it's for a short amount of time and there is extremely good evidence that the criminals are in the area being locked down, I would say yes. Otherwise, no, it's not worth the disruption of people's lives that it causes.
If you build a man a fire, he'll be warm for a day.
If you set a man on fire, he'll be warm for the rest of his life.
Maybe/other. Under most circumstances no, such as a serial killer(if you can call that normal), a guy who killed a specific target, etc.
When you have a situation where suspects could hide in the populace, attacked at random, have non-specific targets, and their motives and MO are relatively unknown then yes, lock the city down.
1) Limited crowds on the streets, they can't blend in.
2) Hopefully limited civilian interaction with the perpetrators, reduces the chance for further casualties.
3) Keeps movement of the populace to a minimum, if you can start to do a sweep you may be able to catch the perps.
It's not optimal and shouldn't be used unless the situation is extreme. However in the Boston incident there's been a lot of damage done, and even police were engaged and injured/killed at random.
Neither side in an argument can find the truth when both make an absolute claim on it.
The principle of martial law has long been used in the US and around the world. Folks are being asked to stay off the streets for a very short time period. This aspect of it (attacking the lockdown) is much ado about nothing.
Unfortunately someone decided that Al Qaeda wasn't a national security issue but a law enforcement issue. The rest is history.
It's all here.-> Bin Laden's Fatwa | PBS NewsHour | Aug. 23, 1996 | PBS