British Colonel Howard Vyse reopened Mamoun’s forced entryway in 1837.
British archaeologist and explorer, Sir Flinders Petrie believed that someone had entered the Great Pyramid before Al Mamoun;
“When, then, was the Pyramid first violated? Probably by the same hands that so ruthlessly destroyed the statues and temples of Khafra, and the Pyramids of Abu Roash, Abusir, and Sakkara. That is to say, probably during the civil wars of the seventh to the tenth dynasties.”
Some researchers today believe that it was first entered shortly after its completion by those who had knowledge of the entryways.