On the surface, John Wayne Gacy seemed a cornerstone of his suburban Chicago community in the 1970s: Gregarious and boastful, he was known for running a successful construction business, his involvement in local politics and, especially, for entertaining young children at parades and hospitals as the jolly clown, Pogo.

However, there were troubling signs behind the makeup for those who bothered to look, from the coming and going of young men from his home at all hours of the night, to the unusual odor that emanated from the bowels of that house, to his conviction for a sexual offense with a minor that nobody seemed to know about.

When the horrific truth finally came out, neighbors were shocked to learn that their once-friendly neighbor was masking the impulses that made him one of the most prolific serial killers in history — and the image of the clown as a happy, beloved entertainer would never be the same.

Watch the special three-night event, Invisible Monsters: Serial Killers in America, beginning Sunday, August 15 at 9/8c on A&E.

1967-68: Gacy is accused of sexual assault

Gacy, a restaurant manager and a father of two in Waterloo, Iowa, sees his family-man image shattered when two high school boys describe to authorities how he served them alcohol, forced them to watch pornographic films and initiated sexual contact; one also claims that Gacy attempted to strangle him. Gacy subsequently hires a high school senior to intimidate one of the boys into remaining silent, a move that backfires.

December 3, 1968: Gacy is sentenced to 10 years behind bars

One month after pleading guilty to sodomy, Gacy earns a 10-year prison sentence, the strict punishment meant to serve as "a further deterrent" to his preying on teenage boys.

June 18, 1970: Gacy is granted parole

Reportedly a well-behaved prisoner, Gacy is allowed to leave the Iowa State Reformatory for Men at Anamosa after just 18 months. Divorced from his wife, and his abusive father now deceased, he moves to his hometown of Chicago to live with his mother.

February 12, 1971: Gacy again draws the attention of authorities

A teenage boy tells Chicago police that Gacy picked him up from a bus station and tried to force him into having sex. The charges are dropped when the boy fails to show up to testify in court, and the incident seemingly escapes notice from the Iowa parole board.

August 1971: The businessman settles in a new home

Needing a larger space to operate his new construction business, PDM Contractors, Gacy and his mother move into a house at 8213 West Summerdale Avenue in Norwood Park Township.

January 3, 1972: Gacy kills his first victim

Returning to the bus station, Gacy picks up his first known murder victim, later identified as Timothy McCoy. After bringing the teenager home, where they drink and engage in sexual acts, Gacy stabs him to death and buries him in a crawl space.

July 1, 1972: Gacy gets hitched again

Gacy marries Carol Hoff, a childhood friend. She notices a strange smell coming from the crawl space, but her husband blames it on the runoff from a sewer pipe, and attempts to stifle the smell by spreading concrete and lime in the area.

July 31, 1975: A young associate of Gacy's goes missing

John Butkovich, one of the many young men and teenagers hired for PDM Contractors, disappears after a heated confrontation with Gacy over unpaid wages. His car is found near his parents' home the following day with the key in the ignition. Butkovich is later identified as Gacy's third murder victim.

January 1976: Police stake out Gacy's home

The complaints beginning to pile up, police camp out at 8213 West Summerdale Avenue after a 9-year-old boy prostitute is reported missing. Attempts to question the young men coming and going from the house fail to uncover any relevant evidence.

John Wayne Gacy house
John Wayne Gacy's house; Photo: Bettmann / Contributor

March 2, 1976: Gacy divorces his second wife

Already living alone, Gacy has his separation from Carol formalized with their divorce. During this time he begins appearing more frequently around town as his alter ego, Pogo the clown. He also picks up the pace on his murderous spree, claiming another two dozen victims from April 1976 through the end of 1977.

March 21, 1978: Gacy attacks a man in his car

After luring Jeff Rignall into his car with an offer to smoke marijuana, Gacy subdues the 26-year-old with a chloroform-soaked rag, tortures and rapes him at his home, and then dumps him out in a park. Rignall, who accepts $3,000 to settle the legal charges, goes on to recount the experience in his book 29 Below.

December 11, 1978: Gacy's final murder victim puts police on his trail

When 15-year-old Robert Piest goes missing after telling his mom he intends to see someone about a high-paying job, police follow the trail of witnesses to Gacy's home. Unlike many of the other runaways and dropouts who wound up in Gacy's clutches in the middle of the night, Piest is a popular high school student with strong ties in the community; Gacy's lawyer later theorizes that his client began getting more careless about his killings with the hope of getting caught.

December 13, 1978: Gacy's home is searched

After initially stalling, Gacy submits to questioning at the Des Plaines police station and hands over the keys to his home. When investigators find a receipt linked to Piest, Gacy is put on around-the-clock surveillance.

December 20, 1978: Gacy reveals his crimes to his lawyer

After a week of being followed, an inebriated Gacy admits to his new lawyer, Sam Amirante, that he had tortured, raped and killed at least 30 young men. An investigating officer later recalled the horrified lawyer's instructions to him: "Don't let Gacy leave!"

December 21-22, 1978: Gacy is arrested, leading to his confession

Gacy is apprehended when seen handing a bag of marijuana to a gas station clerk, prompting another home search that reveals the first discovery of human remains. The following day, the suspect delivers a rambling statement to police in which he confesses to killing more than 30 young men and boys, with most buried in his crawl space and the rest thrown into the Des Plaines River, though Gacy later attempts to retract his confession.

Over the next several weeks, investigators would unearth the remains of 29 bodies on Gacy's property and another four in the rivers southeast of Chicago.

April 23, 1979: Gacy is indicted for a total of 33 murders

After being charged with seven murders in early January 1979, Gacy is indicted for another 26 by a grand jury, the total representing the largest number charged to one person in American history.

John Wayne Gacy victims
Headshots of some of Gacy's victims.; Photo: Bettmann / Contributor

February 6, 1980: Gacy's trial begins

The five-week long trial features the gut-wrenching testimony of Rignall, who vomits on the stand after recalling the tortures enacted on him, and the forensic experts who explain how most of the victims died by way of a rope tightened around their necks. Entering a plea of insanity against their client's wishes, the defense calls on Gacy's mother and sister, who recount the physical and emotional abuses inflicted by his father, as well as several medical witnesses to confirm their findings of Gacy's mental disturbances.

However, the state argues that Gacy was fully capable of comprehending his crimes, with prosecutor William Kunkle dramatically dropping photos of each known victim into the trapdoor of Gacy's crawl space, brought to the courtroom as evidence, during his closing arguments.

March 12, 1980: Gacy is convicted

The jury takes just one hour and 50 minutes to find Gacy guilty of the murders. The following day, the same jury takes 2 hours and 15 minutes to impose the death penalty, drawing applause from onlookers. Afterward, Judge Louis B. Garippo thanks the jury, noting, "Whatever the cost [of the trial], it was a small price... What we do for the John Gacys of this world we will do for everyone."

June 13, 1981: The unidentified victims are buried

Through funds donated by the Funeral Directors Association of Greater Chicago, the nine unidentified Gacy victims are each buried under a headstone inscribed with the words "We Are Remembered." Five years later, one of the bodies is determined via dental records to be that of Timothy McCoy, Gacy's first victim.

March 4, 1985: The U.S. Supreme Court denies Gacy's appeal

The high court rejects Gacy's assertion that his death sentence amounts to cruel and unusual punishment, though dissenter Thurgood Marshall acknowledges that the case raises legitimate constitutional questions, paving the way for Gacy's appeals to drag on for close to another decade.

December 17, 1993: An execution date is set

After another appeal is rejected by the U.S. Supreme Court, the Illinois Supreme Court sets a date of May 10, 1994, to execute the convicted mass murderer.

March 1, 1994: Gacy launches a paid phone line

Having already made waves with his clown-themed paintings and sketches, Gacy further raises the ire of officials by unveiling a $1.99-per-minute telephone line which features a recorded interview of him answering commonly asked questions about the case.

May 10, 1994: Gacy is executed

His last-second attempts at a stay of execution squashed, Gacy is transferred to Illinois' Stateville Correctional Center, where he is reported to be in a "chatty" mood and enjoys a last meal of fried chicken, shrimp, fries and strawberries. After delivering a final statement on behalf of his innocence, the 52-year-old is put to death just after midnight by lethal injection.

October 12, 2011: Illinois sheriff seeks to identify more victims

Armed with new DNA technology, Cook County Sheriff Thomas Dart announces that he has exhumed the remains of the eight unidentified Gacy victims and urges relatives of young men who went missing in the 1970s to come forward and undergo saliva tests. His efforts bear fruit when Victim No. 19 is identified the following month as William George Bundy, and when Victim No. 24 is identified as James Byron Haakenson in July 2017.