I am currently reading a book Burried Secrets by Edward Humes published in1991. It is subtitled A True Story of Serial Murder, Black Magic, and Drug-Running on the U.S. Border. I am currently working on a novel on a pair of Serial/Spree killers in 1799. [If you feel like communicating on the subject of novel writing on dark doings, you can private message me.] This documented story deals with a Cuban/American priest of the black arts, specifically Palo Mayombe, and the mostly white magic of Santeria.
Apparently, magic was becoming ever more popular among drug dealers at that time, and from the bloody doings that have recently surfaced of mass murders, I would not be surprised if it has become much more widespread. The action moves back and forth from Matamoros/Brownsville and Mexico City. I would not be surprised if Nuevo Laredo/Laredo has similar issues. The case was broken when a spring break celebrating college student was kidnapped, tortured and murdered in a Palo ritual. Perhaps you were VERY lucky.