What caused the serial killing spike of the 1970s and '80s?

Murderland: Crime and Bloodlust in the Time of Serial Killers , by Caroline Fraser, Penguin Press, 480 pages, $32

The Pacific Northwest produced an appalling roster of serial killers in the 1970s and '80s, some of whom claimed very large totals of victims. We think immediately of Ted Bundy, but there is also Gary Ridgway, the Green River Killer, with his likely kill count of 50-plus victims; just over the Canadian border, British Columbia produced the serial child murderer Clifford Olson. By some measures, the region is the most prolific in the history of multiple murder.

Observers have often spoken of an "epidemic" with its epicenter at Tacoma, Washington. It is very hard to track serial killings accurately, especially since some styles of murder are more easily detectable in some eras