The reason that police can get away with literally murder is because of a doctrine known as ‘qualified immunity’ that gives wide latitude to police actions taken during the course of their duties. Furthermore, even when they do get sued and fines are levied, the city pays the fines, giving them even more reason to not feel constrained.
Qualified immunity is a judicially created doctrine that shields government officials from being held personally liable for constitutional violations—like the right to be free from excessive police force—for money damages under federal law so long as the officials did not violate “clearly established” law.
…[Q]ualified immunity opponents contend that the Harlow Court got the balance wrong. Justice Sonia Sotomayor—who has called qualified immunity a “one-sided approach” that “transforms the doctrine into an absolute shield for law enforcement officers”—captures the core of that critique in a recent opinion, which Justice Ruth Bader Ginsburg joined. As Sotomayor put it, qualified immunity “sends an alarming signal to law enforcement officers and the public. It tells officers that they can shoot first and think later, and it tells the public that palpably unreasonable conduct will go unpunished.”