The first call, from someone claiming to belong to the Michoacán Family drug cartel, came in February 2015.

"They said they knew who I was and where I lived," said Alberto Arredondo, who got the call at work as a pump technician at an oil refinery in the central Mexican city of Salamanca. "They wanted information."

At first, Arredondo hung up.

"But they were insistent," he said, calling back and demanding details of when fuels would be pumped and through which pipelines.

Over the next two years, Arredondo said, he would be hounded, kidnapped, pistol-whipped and stabbed so severely that surgeons removed his gall bladder. In December 2016, he fled to Canada, where he now seeks asylum from gangs that steal fuel from Salamanca and five other refineries operated by Pemex, the state-owned oil company.