Ronald Clark O'Bryan, nicknamed The Candy Man and The Man Who Killed Halloween, was an American man convicted of killing his eight-year-old son Timothy on Halloween 1974 with a potassium cyanide-laced Pixy Stix that was ostensibly collected during a trick or treat outing. O'Bryan poisoned his son in order to claim life insurance money to ease his own financial troubles, as he was $100,000 in debt. O'Bryan also distributed poisoned candy to his daughter and three other children in an attempt to cover up his crime; however, neither his daughter nor the other children ate the poisoned candy. He was convicted of capital murder in June 1975 and sentenced to death. He was executed by lethal injection in March 1984.

Potassium cyanide is a compound with the formula KCN. It is a colorless salt, similar in appearance to sugar, that is highly soluble in water. Most KCN is used in gold mining, organic synthesis, and electroplating. Smaller applications include jewellery for chemical gilding and buffing. Potassium cyanide is highly toxic, and a dose of 200 to 300 milligrams will kill nearly any human.