Ronald Clark O'Bryan was born on October 19, 1944, in Houston, Texas. He lived with his wife, Daynene, and their two children, Timothy (born April 5, 1966) and Elizabeth, in Deer Park, Texas. O'Bryan worked as an optician at Texas State Optical in Houston and was an active member of his local church, where he sang in the choir and served as a deacon. His life appeared outwardly stable, but he was struggling financially, racking up significant debt.

O'Bryan became involved in a variety of schemes to solve his financial troubles, including taking out large life insurance policies on his children. He was reported to have been struggling with personal and professional difficulties, and in the months leading up to Halloween 1974, he had shown an increasing interest in poisons and chemicals, including cyanide. Despite his seemingly normal public persona, he had a hidden agenda that would soon lead to a tragic and infamous crime.

On Halloween night, October 31, 1974, O'Bryan took his two children, Timothy and Elizabeth, along with a neighbor and his two children, trick-or-treating in Pasadena, Texas. At one house, where no one answered the door, O'Bryan stayed behind while the others moved on. He later caught up with the group, claiming that the homeowner had given him five 21-inch Pixy Stix to distribute among the children.

That evening, Timothy asked to eat some of his candy before bed and chose the Pixy Stix. After tasting it, he complained that it was bitter. O'Bryan gave him Kool-Aid to wash away the taste. Timothy immediately began vomiting and convulsing. He died en route to the hospital less than an hour after consuming the candy.

An autopsy revealed that the Pixy Stix Timothy consumed was laced with a fatal dose of potassium cyanide. The other four Pixy Stix were recovered before any other children could consume them. Investigators found that the candies had been opened, filled with cyanide powder, and resealed with staples.

Initially, O'Bryan claimed he couldn't remember which house had given him the Pixy Stix. After repeated questioning, he identified a house owned by Courtney Melvin. However, Melvin had a solid alibi, as he was working as an air traffic controller and had over 200 witnesses confirming his presence at work during the time in question.

Further investigation revealed O'Bryan's financial troubles and the life insurance policies he had taken out on his children. Witnesses testified that O'Bryan had shown an unusual interest in cyanide and had inquired about purchasing it. He had even visited a chemical supply store in Houston shortly before Halloween but left without buying anything after learning the smallest amount available for purchase was five pounds.

O'Bryan was arrested on November 5, 1974, and charged with one count of capital murder and four counts of attempted murder. His trial began on May 5, 1975. On June 3, 1975, after 46 minutes of deliberation, the jury found O'Bryan guilty on all counts. He was sentenced to death by electrocution.

O'Bryan maintained his innocence throughout the trial and appeals process. He was executed by lethal injection on March 31, 1984, at the Huntsville Unit in Huntsville, Texas. Outside the prison, a crowd of approximately 300 people gathered, some chanting "Trick or Treat!" and throwing candy in protest.