According to police reports, the astonishing multiple homicide occurred in a closed room reserved for conjugal visits between inmates and their partners.
Because of the rainy climate, Domingo Villa Arellano had been allowed to take his wife Erika Isela Velazquez, 39, and their two children, Angel and Valeria, aged 1 and 3, inside the room. Meanwhile, his 17-year-old stepdaughter, Erika Lizeth Ramos Velazquez, waited outside.
Once inside, reports say, an argument ensued and Villar Arellano attempted to strangle his wife before stabbing her repeatedly in the throat with a sharp handmade weapon fabricated from wire. He then stabbed the two infants in the same manner.
Villar Arellano attacked his stepdaughter when she came into the room to see what was happening. Although bleeding profusely from stab wounds, she managed to escape and run for help. According to one report, she was unable to locate any guards, and other inmates rushed to the room to restrain Villar Arellano, who was in the process of trying to injure himself with the weapon.
Velazquez and her children were found lifeless in the room. Her teenage daughter, who had raised the alarm, was taken to hospital but died the next day. Domingo Villar was treated inside the prison and will make a full recovery.
It is still unclear why prison guards failed to monitor Villar Arellano, a former police officer who had been in prison since 2006 for the murder of his first wife and the rape of her daughter.
Neither was Puente Grande Director Angelica Rivera Ortega able to provide an explanation as to why guards were unaware of the events unfolding in the room. Attorney General Luis Carlos Najera later explained that it was not uncommon for entire families to use the conjugal visiting rooms on certain occasions.
Rivera Ortega acknowledged that Villar Arellano probably made the murder weapon from material that was available in prison workshops.
Four prison officers have been suspended in the wake of the incident. Domingo Villar is facing multiple murder charges.