National Human Rights Commission President Luis Raul Gonzalez Perez yesterday said there were also two cases of torture and two more deaths caused by excessive force.
"The investigation confirmed facts that show grave human rights violations attributable to public servants of the federal police," Gonzalez said.
One police officer was killed in the confrontation on May 22, 2015. The government said the dead were drug cartel suspects who were hiding out on a ranch in Tanhuato near the border with Jalisco state.
The lopsided death toll of 42 to 1 had led to suspicions of extrajudicial killings.
The commission's investigation found that 40 of the civilians killed were shot. One died in a fire and another was run over.
The government had refused to release the autopsy reports of the victims. The government's transparency watchdog earlier said there was no evidence to indicate human rights violations.
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