While I appreciate everybody's concern about serious constitutional questions with the way that the Watertown police handled the alleged bomber, I'm also concerned that delays necessary to comply with procedures may have resulted in even more deaths. After all, if I understand the following article correctly, I'm not sure of the condition of one Watertown law-enforcement officer who was seriously injured in confrontation with the alleged bomber.
Lone officer confronted marathon bombing suspects in firefight, chief says
Also, note the last part of Clause 3 of Section 10 of Article I of the Constitution.
Clause 3: No State shall, without the Consent of Congress, lay any Duty of Tonnage, keep Troops, or Ships of War in time of Peace, enter into any Agreement or Compact with another State, or with a foreign Power, or engage in War, unless actually invaded, or in such imminent Danger as will not admit of delay (emphasis added).
Although the clause emphasized above is not directely applicable to the Watertown situation, it reflects that the Founders understood that authorities may sometimes be forced to act because of time restraints.
I was getting ready to post but had an interesting insight. Note that the Founding States had decided that government prohibitions / limitations of power in the Bill of Rights did not apply to the states, only to feds. (14A changed that.) So 4A's privacy protection without warrant originally did not apply to states.
The 4th was incorporated in the 60's. All the cases were specific individuals (e.g. Terry stop) or cars or houses. Houses have the most protection. Any unrelated criminal case arising from Watertown (e.g. if the cops had found drugs after busting into someone's house) would be laughed out of court. There is simply no case law supporting home searches with the few exceptions that only apply to specific houses. The cop must pursue a suspect into a specific house. A cop may have a hunch about a specific house and that is legal grounds (has to be explicit). A cop might see something in the yard or through a window which would make the search legal. Or the cops can get permission from a homeowner or any representative (essentially anyone from a teenager on up can legally let them in). But that is it.
There were large bombs that killed lots of people in the anarchist and communist violence in the 1920s. I don't think the people who were dealing with that decided that the solution was to violate the rights of the law abiding citizens. This is not unique, only the response of law enforcement is new.