Surely would be much more logical than firing shots at suspected terrorists possibily armed with explosives in crowded places? I would have thought that the potential is there to a.detonate the explosives b. kill others in the area and c. kill innocent suspects needlessly?
Tranquilisers might not take effect immediately, which could give the 'criminal' chance to shoot/detonate bomb etc. Head shots are instant.
Paralysing nerve gas It's the future. Or that air compression weapon that causes the target (and anyone near) to spontaneously **** themselves (literally)