Who was the last victim of John Wayne Gacy? Details explored as Peacock drops Devil in Disguise: John Wayne Gacy

Devil in Disguise: John Wayne Gacy opened with the case of Robert Piest, the 15-year-old whose disappearance in 1978 led police to John Wayne Gacy. Piest has long been identified as Gacy’s last known victim, and the investigation into his case broke everything open.

The series arrived on October 16 and used past events to frame a straight timeline. It centered the families, the detectives, and the record. It did so without sensational flourishes, keeping the focus on verifiable details and the consequences of missed warnings.

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Who was the last victim in Devil in Disguise: John Wayne Gacy?

Robert Piest was a high school student in Des Plaines, Illinois. He vanished on the night of December 11, 1978, after a brief conversation about possible work.

Diagram of Gacy's Norwood Park residence, depicting the dimensions of his crawl space (Image via Wikimedia Commons)

His disappearance triggered sustained surveillance on Gacy and a search that uncovered human remains at Gacy’s home. That search ended speculation and set up a criminal case that moved fast.

Piest’s body was later recovered from the Des Plaines River. The recovery helped confirm the scope of the crimes and tied back to statements Gacy gave after his arrest. As WBEZ Chicago reported, the pilot centered on Piest because his case was the clincher that brought the proceedings to a head.

Medical examiners retrieve one of the first bodies exhumed from beneath Gacy's crawl space. December 23, 1978. (Image via Wikimedia Commons)

Also read: How many episodes are there in Devil in Disguise: John Wayne Gacy? Episode count, release schedule, and more

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How Devil in Disguise: John Wayne Gacy presented the Piest investigation

The show traced the early steps with clear beats. Detectives interviewed Gacy, tailed his car, and documented movements. A first search warrant yielded items that raised alarms. A second search warrant took officers into the crawl space.

From there, the series followed the excavation. Viewers saw how identification efforts worked. Dental records. Personal effects. Timelines built from receipts and logs. Each step showed standard casework, not guesswork.

The script also depicted moments in which victims from working-class or LGBTQ+ communities were reportedly dismissed or blamed. The production framed that theme as one factor that allowed a serial offender to operate for years. TV Insider noted that this critique ran through the season while still acknowledging the officers who did the digging and paperwork for months.

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Why Piest’s case mattered in Devil in Disguise: John Wayne Gacy

Piest’s age and clean routine undercut runaway assumptions. A specific timeline anchored by a work shift and a short window gave detectives something to test. Phone calls. Store records. Witness statements.

Evidence then stacked up. Surveillance teams logged Gacy’s movements. Dogs alerted to a vehicle. A rancid odor noted by an officer near a vent pointed the team back to the house. Each piece added weight.

Once the crawl space search began, the case turned from a missing-person file into a serial homicide investigation. The pace changed. So did public attention. Court filings followed, and prosecutors moved on 33 murder counts.

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About Devil in Disguise: John Wayne Gacy

The series drew from a 2021 docuseries but dramatized events with emphasis on victims and process rather than gore. It stressed names, dates, and the work needed to identify people still listed as John Does.

Devil in Disguise: John Wayne Gacy premiered on Peacock on October 16 and spans eight episodes covering the Piest lead, the search warrants, and the courtroom outcome.

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Edited by Preethika Vijayakumar