A group of 34 of America’s biggest cities suffered a 30 percent total increase in homicides in 2020, according to a new survey published Monday, with police in four Midwestern cities reporting increases of more than 60 percent over 2019.

The two epochal events of 2020 — the coronavirus pandemic and the nationwide protests over police violence — were likely factors in the increase in slayings, two of the report’s authors said. The pandemic limited proactive anti-crime strategies by both police and social workers, commission director Thomas Abt said, and reduced focus on urban hot spots known to be large sources of violence.