A reader floats a plausible theory:
As much as it pains me to say it as a privacy advocate, I would like to suggest that the decline in crime rates starting in the ‘90s might have to do with the ubiquity of video cameras.
Personal camcorders were invented in the mid-’80s, with a subsequent rise in closed circuit television (CCTV). In the early ‘90s, multiplexing was introduced for CCTV, meaning that additional cameras could be recorded on the same tape, with a concurrent increase in the number of security cameras actually deployed. By the mid-’90s, every ATM had a camera. The 2000s brought the advent of digital photography and video in the early years, with cellphone cameras and video in the latter. I suspect that if one were to plot the number of video cameras per capita on a national basis, you would see a very sharp rise starting in about 1990.
We’ve seen over the past year how the ubiquity of cellphone cameras has exposed police injustice, and before that there was the demand to add video recording to police vehicles after the nation watched video tape of the Rodney King beating. It seems therefore quite plausible to me that the decline in the crime rate over the past two and a half decades could well be explained by the expansion of surveillance, rather than the continuing expansion of incarceration.