These mummies were discovered, when the government ordered a tax on a cemetery which caused the families to dig up their relatives from the ground. Since certain families had paid the taxes, most of the bodies become disinterred. As a result, only 2% of them had been mummified.
The people buried were not purposely turned into mummies, it was because of the dry weather in Mexico that resulted in the bodies turning into mummies.
All these mummies were a cause of the cholera epidemic that hit Mexico in the year 1833.
Additional Information Edit
The mummies were stored in a building that is now currently a museum. The museums name is El Museo De Las Momias, also known as the "Mummies Museum".