Serial killer John Wayne Gacy's sickening final words proved he showed no remorse for his crimes

The final moments before the execution of a serial killer can be a moment when they finally show some remorse.

But for serial killer John Wayne Gacy this could not be further from the truth, as the his last words made abundantly clear.

Gacy was born in Chicago in 1942 and built up a reputation in his community as a clown, where he would perform at charitable events and children's parties.

Behind this wholesome exterior however, Gacy concealed a deeply sinister secret.

A sadistic streak led to him being convicted of sexually assaulting a teenage boy in 1968, before being confined to Iowa State Men’s Reformatory, where he underwent psychological evaluation.

He was released in 1970 and arrested for another sexual assault while still on parole, though the charges would be dropped and he would become an independent contractor and buy a house in Chicago.

It wouldn't be until eight years later in 1978, that the full horror of Gacy's crimes would come to light.

Gacy's crimes were discovered in 1978 (Bettmann / Contributor / Getty)

Over the intervening eight years the house developed an unpleasant smell, which Gacy claimed was due to damp problems.

In fact, the stench was the result of 29 bodies which had been buried around the property over the years, beginning to decay.

Police discovered the bodies after one of Gacy's victims, Robert Piest, was reported missing and they found that Gacy had been the last person to see him alive.

They also found a further four bodies in the Des Plaines River, which was located nearby.

Despite the overwhelming evidence Gacy would plead not guilty to the charges, claiming insanity.

A number of psychologists described Gacy as schizophrenic, but the evidence was rejected by the jury and he was convicted of all 33 murders and sentenced to death.

Gacy was executed in 1994 (Bureau of Prisons/Getty Images)

In 1994 Gacy was executed by lethal injection, with his last words confirming that he felt no remorse for his actions.

Reportedly telling officers to: 'Kiss my ass.'

However, a prosecutor who attended the execution claimed that he had not spoken in his final moments.

Gacy committed his first known killing in January 1972 when he stabbed 16-year-old Timothy McCoy to death.

The killer had lured McCoy to his house for sex and reportedly attacked him when he saw him standing in a doorway holding a knife.

After the killing, Gacy claimed that he had gotten a thrill from the murder.