Riddle didn't learn the complete story of his birth until he tracked down and visited his uncle Morfin Gaunt the summer after Myrtle died. In revenge for his father's abandonment and Muggle blood, he went to the Riddle mansion in Little Hangleton and murdered his father and grandparents. Around 1943, in the summer, Tom went to Little Hangleton to learn about his mother's family. While there, he met his uncle Morfin Gaunt, with whom he was far from impressed. Morfin mentioned offhandedly at one point during this meeting that he thought that Tom looked "mighty like that Muggle," Merope's husband, Tom Riddle Snr. Tom immediately demanded the identity of the Muggle in question, and Morfin told Tom the story of his Muggle father, which infuriated Tom to the point of seeking revenge. Tom stunned Morfin and took his wand, went to the Riddle House and, using his uncle's wand, murdered his father, grandfather, and grandmother with the Killing Curse.
He covered up his crimes by altering Morfin's memory, causing him to believe that he was the killer. When the Ministry of Magic investigated the crime, Morfin, who had previously served three years in Azkaban for using magic in front of and against Muggles, freely admitted to the deed and was sentenced to life imprisonment in Azkaban. Tom took the family signet ring from Morfin and wore it like a trophy at Hogwarts.

The Riddle's gardener, Frank Bryce, later told police that on the day of the Riddle's deaths he had seen a stranger; a teenage boy, dark-haired and pale, near the manor. The next morning a maid found Tom Riddle Sr. and his elderly parents dead in their drawing room, "still in their dinner things." The Riddles were as cold as ice and each had a look of terror upon his or her face but had no sign of physical injury. The Riddles were buried in the Little Hangleton churchyard.