State prosecutor Daniel de la Rosa Anaya said the suspect was also an American, but did not identify her.
News outlets in Charlotte, North Carolina, reported that the people Robinson was traveling with gave differing versions of how she died, but that an autopsy revealed she died of a severe spinal cord or neck injury.
A video apparently taped at the luxury villa in San Jose del Cabo shows one woman, apparently an American, beating another woman identified as Robinson.
The video has been reposted many times on social media sites. In it, a man with an American accent can be heard saying, “Can you at least fight back?” The man did not appear to intervene in the beating.