Suspected drug traffickers carrying automatic weapons broke into a Rio de Janeiro sport complex built for the 2016 Olympics to play in the swimming pool - where they posed for a group photo.
Brazilian authorities said they are investigating the incident allegedly involving members of the infamous Amigo dos Amigos (ADA) drug gang, which has its stronghold in the northern favela of Pedreira.
The break-in at the Vila Olímpica Félix Mielli Venerando occurred last week but emerged only later, when a photo depicting the suspect gangsters holding up their rifles in the Olympic pool circulated on social media.
Detectives said they suspect the mobsters posted the photo online to show off their firepower, Folha de S. Paulo newspaper reported.
Authorities said the venue, built in 2012 to host the next Summer Games, was closed at the time of the trespassing and security has been since stepped up.
Police believe the pool-party gunmens' leader is a renewed gangster named Celso Pinheiro Pimenta, aka 'Playboy'.
He was heard talking about the Olympic venue in a conversation taped by police.
"I loved the pool," he told another mobster, Jornal do Brasil newspaper reported.
Brazilian authorities have put a reward of20,000 Reals (£5,000) on his head.