Mexico's federal police arbitrarily executed 22 people on a ranch in the western state of Michoacán last year, the country's human rights commission said Thursday.
National Human Rights Commission President Luis Raúl González Pérez 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," González 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 commission also threw doubt on the government's explanation of what led to the clash in the first place. Federal police had said they encountered a truck and took fire from its passengers before being led to the ranch.
The commission's report said the government did not produce evidence that supported that account.
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.