The murder rate is still low compared with previous decades, and other types of serious crime have dropped in the past few months. But researchers, police and some residents fear the homicide spike, if not tamed, could threaten an urban renaissance spurred in part by more than two decades of declining crime.

A Wall Street Journal analysis of crime statistics among the nation’s 50 largest cities found that reported homicides were up 24% so far this year, to 3,612. Shootings and gun violence also rose, even though many other violent crimes such as robbery fell.

Police, researchers, mayors and community leaders see a confluence of forces at work in the homicide spike. Institutions that keep city communities safe have been destabilized by lockdown and protests against police. Lockdowns and recession also mean tensions are running high and streets have been emptied of eyes and ears on their communities. Some attribute the rise to an increase in gang violence.