According to police, a drug-trafficking outfit from the slum next to the prison orchestrated the attack in an attempt to break out 18 inmates, who were waiting for their accomplices in the penitentiary's courtyard. Around 40 gunmen from the gang that controls the Morro do Zinco neighborhood in northern Rio attacked a police post next to the back wall of the Milton Dias Moreira prison. After expelling the police, gunmen threw ropes over the wall into the prison, while others attacked the guard posts on the sides of the facility. Guards fatally shot two prisoners scaling the wall, but four inmates managed to get away. Twelve prisoners unable to reach the ropes to climb the 10-meter (33-foot) barrier were captured and found to be carrying two firearms and two grenades that had been thrown over the wall by their accomplices. Police had to detonate one of the grenades inside the prison. The shootout lasted for nearly an hour and sparked panic among residents of Morro do Zinco. Mass escapes and riots have become commonplace in Brazil's overcrowded prisons, which house more than 300,000 inmates in facilities built to hold 192,000. Authorities acknowledge that several of the country's penal facilities are controlled by organized crime rings, whose leaders continue to run their drug- and arms-trafficking businesses from behind bars. In June, a turf war between rival drug gangs triggered a grisly massacre in northern Rio's Benfica prison that left 30 dead.