In four different prisons in the Brazilian capital of North Amazon, nearly 60 inmates were killed within two days, according to the authorities.
State Department of Prison officials said they had found at least 40 inmates in three different prisons They were in Manaus on Monday and all showed signs of suffocation.
They died only one day after fifteen inmates were killed in an uprising in Manaus prison complex Anisio Jobim – 56 prisoners died from similar violence two years earlier.
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While little information was released about the murders on Monday, local officials indicated that the prisoners were absent during the visiting hours at Anisio Jobim Sunday lunchtime fought each other.  They said security reinforcements had invaded and regained control within 45 minutes.
"Everyone began to run, and everyone hit the cell doors, the doors and ran down the corridors," said Colonel Marcus Vinicius, who, according to the BBC, is responsible for the prisons in the Amazon state. "It was not a rebellion, it was fighting among inmates."
The killers were either smothered or stabbed in front of the visitors with toothbrushes, the Independent reported.
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On Monday, 25 inmates were killed in the Antonio Trindade Penitentiary, six in Puraqueruara Prison. According to the Brazilian Ministry of Justice and Public Security, five more were killed in the makeshift detention center and another four in Anisio Jobim.
"I have just spoken with (Justice) Minister Sergio Moro, who is already sending a Prison Intervention Team to the state of Amazonas to help us with the crisis and a national problem: the problem of prisons," he said Governor of Amazon, Wilson Lima.
These incidents were not the first time that violence broke out in the city's prisons.
In early 2017, more than 120 inmates died from other prisoners during several weeks of fighting between rival criminal gangs. Many of these victims have their heads cut off or their hearts and guts ripped out.
Several drug traffickers and criminal gangs in Brazil do most of their daily business in prisons. The authorities have not said if gang wars are behind the last blood poisoning.
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Moro had to send a federal task force to tame the violence in the state of Ceara in January, local officials said, ordered by leaders of crime groups to be annoyed at plans to impose stricter controls in state prisons.
The Associated Press contributed to this report.