Communications gaps, unguarded warehouses and a lack of written instructions opened an opportunity for a gunman at a rally in Butler, Pa., in July.

© Kristian Thacker for The New York Times

Officers fired during a clash with a man carrying a knife who was first stopped for fare evasion, police said. Two bystanders, an officer and the man were struck.

© Dave Sanders for The New York Times

Kim Potter, who fatally shot Daunte Wright during a traffic stop, had been scheduled to talk to officers in Washington State about the use of force.

© Aaron Nesheim for The New York Times

Under President Nayib Bukele, Salvadorans have swapped their rights for quiet streets. How long can that trade-off be maintained?

China has been considered relatively progressive on juvenile justice. But several high-profile killings have prompted calls for the law to come down more harshly on minors.