The rise of right-wing movements like the "sovereign citizens" – two of whose members were involved in a double police homicide in 2010 – is part of the equation, as is the expanding availability of guns and the growing willingness of armed citizens to use them. But a steady increase in the number of justified homicides by police officers in recent years has also served to "heighten tension" between cops and the communities they serve, says Al Blumstein, a criminal justice expert at Carnegie Mellon University in Pittsburgh.
Interestingly, the spike in police officer deaths does not correspond with violent crimes and homicides in the rest of society, which have steadily dwindled over the past decade from around 8 homicides per 100,000 Americans to fewer than 5 per 100,000 last year. So what gives?
'Exceedingly hostile' malcontents
"There is a contingent of malcontents out there who are exceedingly hostile," says Rich Roberts, a spokesman for the International Union of Police Associations. "It's a really complex phenomenon in that it's a whole combination of factors where on one end you've got people like sovereign citizens, who are actually deliberately targeting police, as opposed to your garden variety bad guy who's carrying a gun and will not hesitate to use it."