The sun had only just begun to inch over Rio de Janeiro’s horizon when it began. On October 28, in the tangled shantytown of flimsy dwellings that cluster beneath a Baroque church in the Penha neighborhood, thousands of heavily armed police quietly assembled to carry out what would become the largest police massacre ever recorded in the state of Rio.

Residents of the Complexo do Alemão and the Complexo da Penha — two of the city’s most impoverished and embattled favelas and strongholds of the Red Command gang — were jolted awake by the whir of helicopters and armored vehicles, which provided cover for officers on foot rushing in from the northeast as other battalions closed in from the north and west. Over the next fifteen hours, state forces skirmished with alleged gang members, encircling them and driving them up a steep hill where additional officers — from a unit notorious for its brutality — waited with machine guns and sniper rifles.

Videos that circulated online stunned even those accustomed to the bloodshed of Rio police raids. Sandwiched between the two hills, the densely packed neighborhoods were lit by dozens of flaming vehicles that gangs had torched to slow the police advance. In one clip, officers unleash sustained bursts of fully automatic fire down a slope toward clusters of homes, tracers streaking through smoke. In another, residents crouch inside dwellings of hollow ceramic brick, quivering as rifle fire cracks nearby. Elsewhere, police film themselves clearing bullet-ridden houses like Marines moving through Fallujah.