A spokesman for police in the Caribbean state of Quintana Roo says staff at the prison in Chetumal noticed that the woman seemed nervous and was pulling a black, wheeled suitcase that looked bulky.
Spokesman Gerardo Campos said that prison guards checked the bag of 19-year-old Maria del Mar Arjona and found inmate Juan Ramirez Tijerina curled up inside in the fetal position.
Ramirez is serving a 20-year sentence for a 2007 conviction for illegal weapons possession.
Arjona was arrested and charges are pending.