Good question! It seemed to me that we were discussing something like the last 4-5 years at minimum, because the author identified a prior and continuing decline in surveyed trust of government and institutions, with especially low reported trust during that period. So I would think it helpful to look at homicide rates over the last decade or so for context.

If we think 538 is a reputable source, maybe we could try this: https://fivethirtyeight.com/features/the-u-s-murder-rate-is-...

It seems like there was a gradual decline from a ~9.7/100,000 in 1990, to about ~4.8/100,000 in 2014, followed by a smaller but sharp uptick of about %9-%10, to 5.3/100,000 as of 2016.

Edit: bad math.