Locking up people in prisons would stop street crime, too.
Stop question and frisk was a way of doing it without further crowding our prisons—and without the crime you have prevented by the practice. You establish an attentive presence on the street and they leave the guns at home.
Unfortunately, we have a culture of leniency and phony grievance-mongering toward criminals among our judges and other political types, and they managed to do away with this harmless crime-prevention policy.