The mysterious killing of 17 people in Mexico’s Michoacán state has shocked people in the North American country, prompting local authorities to order an investigation into the gruesome incident.

A once-standout US narcotics agent sentenced to a 12-year prison term admitted to his crimes but blamed former DEA colleagues for fostering a culture of corruption that desensitized him to the implications of violating the law.

At least eleven people were killed in two separate armed attacks in Mexico, officials said on Monday.