On the eleventh of February, 1910, second year Hufflepuff Edward Elric and his first year brother, Alphonse Elric, performed human transmutation in the common room of their house.
In the incident, Edward Elric lost his right arm (at the shoulder) and his left leg (at the knee). Alphonse Elric's body had been replaced by a suit of armor from Hogwarts corridors.
Hufflepuff prefects Theodore Milligan and Winona Laiken discovered the brothers within minutes of the incident and retrieved the school's nurse, Madam Laurel Tooley. After deemed medically stable, both Elrics were expelled from Hogwarts and guided back to their home in Resembool, Amestris.
Investigation found that they had brought their mother's ashes at the beginning of the school year, as well as materials of the human body (such as pneumonia and iron) which they had purchased at Diagon Alley.
Despite prior alchemical knowledge, the Elrics did not perform human transmutation until after studying under Professor Ishmael Grimes, leading to his arrest and the barring of alchemy at Hogwarts School of Witchcraft and Wizardry. Grimes was released when it was deemed that the Elrics had not been taught human transmutation by him, but through their own research.
Alchemy was not reinstated at Hogwarts until the fall of 1956, and only permitted as an elective for sixth and seventh year students.
No information has been provided to the wizarding world on the states of Edward and Alphonse Elric since their being expelled, however, tall tales are spread of an Amestris state alchemist and a man in a suit of armor that many believe to be the Elrics.
Hogwarts has also not been reimbursed for the suit of armor.