37 killed in 3 days in Brazilian city

Thirty-seven people were killed in three days in the Brazilian city of Manaus, and one hypothesis being considered is a coordinated wave of attacks involving police, an official said.

Evidence has emerged over suspects in some of the killings that occurred from Friday to Monday evening in Manaus, a river port in the middle of the Amazon rainforest, said Sergio Fontes, secretary of public safety in Amazonas state, the capital of which is Manaus.

Of all the killings, 35 were by gunfire. From Friday to Saturday alone 23 people died, Fontes said.

He said there were signs the killings were coordinated, although no hypothesis is being ruled out.

Fontes told the news website G1 that the killings could stem from revenge for the death Friday of a military policeman or from fighting among gangs operating both inside and outside prisons.

The firearms used in the killings are used exclusively by the police.

"It is an indication. I am not ruling out that line of investigation ... but I do not want to reach any conclusion until we complete the investigation," Fontes said over the weekend.

Manaus is a violent city, with a homicide rate of 37.4 per 100,000 inhabitants in the period 2010-2012, according to a study the government carried out along with UNESCO. The rate for the country as a whole in that time span was 19.7 per 100,000 inhabitants.