The Last Witness: How a Teenage Girl Helped Catch a Serial Killer

In the winter of 1978, what started as an ordinary shift at a local pharmacy became the final chapter in a young boy’s life and the beginning of the end for one of America’s most notorious serial killers. Kim Byers was working alongside her childhood friend and classmate, 15-year-old Robert Piest, at Nisson Pharmacy in Des Plaines, Illinois when a heavyset contractor with silver-streaked brown hair walked in. The man claimed he needed to take measurements for a potential remodeling job. There was something unsettling about him—he refused to acknowledge Byers when they bumped into each other in the aisles, his “dark omen indigo” eyes avoiding hers. Little did she know that this seemingly mundane encounter would later prove crucial in capturing John Wayne Gacy, a man who had already murdered dozens of young men and boys throughout the Chicago area in the 1970s.

That December evening was meant to be special—it was Robert Piest’s mother’s birthday, and the teenager was eager to get home for the celebration. Before taking out the trash at the end of his shift, he had borrowed back his blue parka from Byers, who had been wearing it while filling out a film development form she had slipped into the pocket. When the contractor returned to retrieve a forgotten appointment book, he lingered, watching Piest with calculating interest. Noticing the boy’s strong work ethic, Gacy approached him with an enticing offer: a summer construction job paying $5 an hour, double the minimum wage. The promising opportunity was enough for Piest to briefly delay his return home. He assured his anxious mother he would be back soon to help blow out her birthday candles. It was a promise he would never fulfill. Piest left the pharmacy with Gacy and disappeared into the night—becoming what investigators would later determine was Gacy’s final and youngest known victim.

When Piest failed to return home, authorities began investigating his disappearance. The day after, an officer visited Byers, informing her that her friend had never made it back to his family. Despite being just 17 years old during a time when young women’s voices weren’t often taken seriously, Byers didn’t hesitate to cooperate with investigators. Her memories of that night, particularly the film receipt she had placed in Piest’s parka pocket, would become a critical piece of evidence. When police confronted Gacy, he adamantly denied ever meeting Piest. But the receipt from Nisson Pharmacy, found among Gacy’s possessions, exposed his lie and gave authorities the grounds they needed to increase surveillance on him. The discrepancies in his statements, coupled with mounting evidence, eventually led to a full search of his home—revealing horrors beyond imagination.

Behind the ordinary facade of Gacy’s residence lay disturbing signs: clown paintings adorning the walls, a hallway painted in bizarre yellow-and-brown zigzags, and most ominously, a trap door leading to a crawl space beneath the home. As investigators searched the property, they discovered grim mementos of lives cut short: a high school class ring, handcuffs, a pistol, and various IDs that didn’t belong to Gacy. When authorities began digging beneath the house, they made the gruesome discovery of multiple bodies stacked in the crawl space. Gacy had literally run out of burial space beneath his home, forcing him to dispose of his later victims in the nearby Des Plaines River. Among the items recovered during the investigation was Piest’s blue parka—silent testimony to the teenager’s fate. After extensive searches, Piest’s body was eventually recovered from the river and identified through dental records.

The story of Gacy has often been mythologized in popular culture, portrayed as a calculating predator who lived a double life as “Pogo the Clown” at children’s parties. However, Byers’ daughter, Courtney Lund O’Neil, who wrote a book called “Postmortem” exploring her mother’s connection to the case, cautions against elevating such killers to celebrity status. “I believe he managed a KFC. So what?” she explained. “He had his own construction business. Well, a lot of people do that… None of this is interesting on its own. Even when they later studied his brain, there was nothing interesting to be found. It was quite a bland, boring brain.” What made Gacy dangerous wasn’t any extraordinary quality but rather his ordinary charisma and manipulative abilities that allowed him to hide in plain sight. As O’Neil notes, “With today’s technology, Gacy couldn’t do any of this successfully.”

In 1980, Gacy was convicted of killing 33 young men and boys, making him one of America’s most prolific serial killers. He was executed by lethal injection in 1995, but the shadow of his crimes continued to haunt those connected to the case. For Kim Byers, the loss of her friend Robert Piest—a nature-loving boy on the path to becoming an Eagle Scout, with dreams of buying a Jeep when he turned 16—remained a painful memory that shaped her life. The trauma influenced how she later raised her own daughter, always warning her about the dangers that might lurk behind friendly faces. When Byers testified at Gacy’s trial, she tried to make eye contact with the man who had taken her friend, but he refused to look at her—perhaps the final act of cowardice from a man who had caused so much suffering. What stays with Byers most poignantly about Robert isn’t the terrible circumstances of his death, but the brightness of his life—his love for his family, his enthusiasm for school and outdoor activities, and all the unfulfilled potential of a life cut tragically short by a chance encounter with evil on an ordinary December night.