Many young people who came to New York for the first time felt this way when they saw that prosperous cosmopolitan: If you made it to New York, you had conquered the world.
Perhaps only after going through certain things did they realize that what they had once taken for granted was not so natural after all.
How could American police not have an obligation to protect citizens from criminals? That was not how it was portrayed on television at all.
Perhaps the police investigations in movies were thrilling, using all kinds of advanced technology or Psychoanalysis, practically miraculous. Yet the case clearance rate of American police was indeed not high.
As long as they did not open a case, the denominator became smaller. That was also one way to raise the clearance rate. What was more, sentencing laws differed from state to state. Some states retained the death penalty while others did not. A good lawyer could render all the evidence law enforcement had painstakingly gathered useless. And the handover process for interstate cases was no different from crossing national borders, invisibly making cases harder to solve.
Obstacles in administration and the judiciary tied the police's hands. Besides, America's political system did not support dictators. Many dictators used the judiciary and police to eliminate their political opponents. Unless a citizen was a state's witness in a major case, the police would provide a safe house and protection detail, even fabricate a new identity and relocate them elsewhere. The chances of that happening were extremely low, low enough to be material for a movie. Only after a citizen had been killed would the police use a criminal case as grounds to arrest or shoot the offender.
Anyone who accepted these rules of the game had to guarantee the authorities' conduct.