In interviews with community leaders, lawyers, security specialists and bereaved relatives, the Guardian pieces together how an operation targeting a criminal gang left 122 people dead last October

• Warning: contains graphic images

• Visual investigation: how Rio’s deadliest police raid unfolded

• The Long Wave newsletter: ‘It doesn’t shock that it’s Black people getting killed’

Juliana Conceição startled awake as the first shots of an infamous day were fired in the Complexo da Penha, the labyrinthine Rio favela where she was born and raised.

It was 4.30am on 28 October. Thousands of police had surrounded the community’s barricaded entrances and were preparing to swarm up its streets on foot and in black armoured personnel carriers with firing ports and bullet-cracked ballistic windows.