Criminologists studying the rise in the murder rate point to the effects the pandemic has had on everything from mental health to policing in a time of social distancing, with fewer officers able to perform the up-close-and-personal community outreach work that in normal times has helped mitigate violence. Experts also attribute the rise to increased gang violence and a spike in gun ownership, including among many first-time gun owners…

Jeff Asher, a crime analyst in New Orleans, said the rise in killings was hitting all corners of the country. He pointed out several Republican-led cities that have seen sharp upticks: Lubbock, which has seen 22 homicides, compared with nine in the same period last year; Lexington, where homicides are up 40 percent; and Miami, where homicides have risen nearly 30 percent.

“Because the stresses of the pandemic are everywhere, you are seeing this everywhere,” he said. (Mr. Asher has published some of his research in The New York Times.)