A decline in policing, or a decline in witnesses? In The Washington Post, the journalist Radley Balko cites research suggesting that the presence of unofficial “sentinels,” such as private security guards and neighborhood watches, exert a similar deterrent effect on crime as the police. Last year, of course, as the coronavirus prompted social distancing restrictions and business closures, people — including potential witnesses — retreated from public space.

Balko believes this can help explain why murder — which tends to be fueled by domestic violence, gang conflicts and drug trading — increased while other crimes more dependent on public interactions fell. “Officials in cities that saw some of the largest murder surges in 2020 and 2021 — including Albuquerque, Indianapolis, Chicago, Los Angeles and others — all have said much of the spike could be attributed to drug- and gang-related murders,” he writes. “So the events of 2020 produced conditions that both encouraged turf wars and gang rivalries, and at the same time undermined the single biggest deterrent to public violence — the presence of witnesses, whether they were police or bystanders.”