Mexico City: Mexico`s human rights commission formally opened an investigation on Tuesday to determine whether federal police committed any abuses in a shootout that killed 42 drug cartel suspects and one officer.
The governmental National Human Rights Commission said it requested "detailed reports" from the authorities to "find out the truth" about what happened in the May 22 gunfight in the western state of Michoacan.
"The gravity and dimension of the accusations being made require that the investigations be conducted as fast as possible," the commission said in a statement.
Federal officials rejected suggestions on Monday that any of the suspects were executed by the officers on a ranch, saying that forensic tests showed all 42 had fired weapons after refusing to surrender.
Authorities suspect the Jalisco New Generation drug cartel, which has killed several security forces in recent months, had taken over the ranch in Tanhuato, near the border with Jalisco state.
Security experts and relatives of the dead have cast doubt over the official accounts, questioning why only three suspects surrendered and why none was found wounded.
The national and Michoacan human rights commissions sent officials to the ranch hours after the gun battle ended.
The commission said it "rejects the climate of violence and lack of security" in some states and said "several events demand to be completely cleared up, like those in Tanhuato and Apatzingan on January 6."
Prosecutors and federal police internal affairs are investigating media reports that officers killed 16 unarmed civilians in Apatzingan, a city in a Michoacan region where vigilantes rose up against the Knights Templar drug cartel in 2013.
Officials said in January that nine people had died in the crossfire of a shootout between police and some of the former rural militiamen.
