This movie is even better than when it first came out in 1974. Those of us old enough to have seen it then can understand what I am talking about. There was a great deal of 70s mentality in this film hence the term Zeitgeist. Urban squalor, violence, apathy, and fear permeate this movie, and were big political issues at the time. During the police investigation, one of the key suspect groups suggested by the Chief of Police was the Vietnam vet - nothing like serving your country faithfully. The Vietnam War was just over, and the Vietnam vets were viewed as potential psychos for any number of reasons real or imagined. The police in NYC are always an easy target, and are shown as being ineffectual. In one scene on the subway, two thugs enter the car, and the cop moves away from them to another car.
As the movie unfolds, Bronson's wife is murdered and the daughter is raped into catatonia during a robbery at their apartment. Bronson feels hopeless for a time after dealing with the system. A work related trip to Tucson breathes some life into him. He comes back to NYC with a pistol a client had given him as a surprise gift. One night while walking, a junkie tries to rob him, and becomes Bronson's first vigilante kill. Thereafter several shooting and deaths occur as others try to rob him. The police figure out that they must have a vigilante on their hands -- even a blind pig can find an acorn. The crime rates plummet, people begin to stand up to the muggers, and the cops start getting scared.
By some miracle, the police trim the list down to Bronson. The Police Chief in charge of the investigation is called in by the DA and other bigwigs for a chat. They tell the Chief that they don't want the vigilante because of all of the publicity the he has gotten. Apparently the public loves him, and cops don't want to look really bad by not being to protect people and then arresting the one person that is fighting back and inspiring others to do the same. They instruct the Chief to "scare him off".
The Chief tries to scare him off, but only makes his point after Bronson has been shot and has no other choice. Bronson makes a bon mot by stating the obvious -- get out of town before sundown.
This movie, while presenting all the darker elements of human nature, is a good movie from a historical perspective and proving once again "revenge" will always sell theatre tickets!