Percius Malfoy was a student at Hogwarts School of Witchcraft and Wizardry . He was son of Nicholas Malfoy, a Malfoy famously known for killing Muggles under the guise of the Black Plague. Percius is infamously known for his murder of Hogwarts potions teacher Afius Dalymore.
Not much is known about Percius's early life (records were not well kept in those days). The only sources of his existence are in the Hogwarts Pensive and in the book The Memoirs of Istaborn Tiberfoot. It is assumed that Malfoy was born in 1340 to Nicholas Malfoy and an unnamed wife. It is known that he was sorted into Slytherin, as was the rest of his family.
Poisoning of Afius Dalymore
During the 1354-1355 school year, in the month of October, Afius Dalymore was poisoned and killed. During the first class of the day, he poured mead into his mug before the class started. He took a swig, and stood up to start class. As he began to speak he got into a coughing fit and began to cough up blood. He fell into his chair and continued to cough until he suddenly stopped. Four students, including future Headmaster Istaborn Tiberfoot, rushed to his side. Dalymore had fallen face first on his desk, and the students pulled him back into his chair. He did not move. One of the four students, who's name was Helda Baggin, ordered two students who were still seated to go get help. The students rushed out into the hallway and alerted then Headmistress Phyllida Spore and her Deputy Headmaster Apin Sommerblott (who happened to be walking down the hallway in a deep conversation).
Spore and Sommerblott rushed into the room and over to Dalymore's body. Spore checked his pulse and pronounced him dead at the scene. She then told Sommerblott to alert the prefects and tell them to take all the students back to their dorms. She also demanded all classes be canceled until further notice. The students in the potions classroom also were sent back to their dorms for their safety. After all students were safely in their dorms, the professors scoured the school to make sure nothing out of the ordinary was in the school.
Investigation and arrest
After the school was declared safe, the professors went to the Teachers Lounge and held a meeting on what had happened. There it was revealed that Professor Revus Caman had spotted a student who had short blonde hair (Percius) entering the potions room fairly early in the morning before class, though Caman only saw him from behind, therefore no arrest could be made. At the meeting, Spore announced that she would alert the Wizards' Council of the murder.
The next day, during dinner in the great hall, Council Chief Crassus Dillard and two Council Officials (today's equivalent of a wizard police officer) arrived at the school. The two officials acted as body guards for Dillard. Dillard approached the professors table and told Spore he was here to investigate and offered to tell the students what had happened. Spore turned down the offer and said she would tell the students herself. She stood up and began to tell the students what happened when Caman noticed the boy sitting at the Slytherin table. He interrupted Spore and shouted "there, thats the boy I saw enter Dalymore's room that morning!" Malfoy, hearing this, bolted out of the great hall. The officials (who had been informed of the evidence) chased after him. When they got close enough, one shot a spell at Malfoy, knocking him face first on the ground. The guards caught up to him and bonded him with a bonding spell.
Spore and Crassus soon arrived in the hallway and watched as the two officials pulled Malfoy up from the ground. Once Malfoy was off the ground, Spore asked him if he had killed Dalymore. Malfoy admitted to it, and when he was asked why, he said he did it because Dalymore was a half-blood, and only pure-bloods should be teachers.
Malfoy was imprisoned at an unknown location. Istaborn Tiberfoot suggested that he was still imprisoned when Tiberfoot was writing his book (written from 1483 to 1490). It is unknown when Malfoy died, and it is also unknown if he died in prison.