Federal prosecutors in Mexico said they believe that 14 of the women slain in the border city of Ciudad Juarez may have been killed in order to sell their internal organs.
Dozens of other women have disappeared.
At least one suspect may be American, those familiar with the investigation said.
Two Mexican suspects were reportedly being held. The theory sparked disbelief among many because none of the bodies found previously had been reported to be missing organs. Many were merely skeletal remains, however.