'I'll be back': Serial killer murderer Aileen Wuornos. Photo / AP

They are some of the most evil individuals on earth, executed for horrific crimes against men, women and children.

Many had decades to think about their terrible acts while waiting to die on death row and as they were being strapped into the electric chair or being prepared to receive a lethal injection, these convicted murderers had one final thing to say.

Clarence Ray Allen

Clarence Ray Allen hired a hit man to kill eight witnesses who testified against him during his trial for the 1974 murder of his son's girlfriend.

A paroled fellow inmate later killed three of them and was arrested in possession of Allen's hit list, which was used to convict him.

He died by lethal injection on January 17, 2006.

Last words: "My last words will be, Hoka Hey, it's a good day to die," he said. "Thank you very much, I love you all. Goodbye."

William Bonin

Convicted of the murders of 14 men and boys between 1979 and 1980 but suspected of raping and killing many more, Bonin was nicknamed the "Freeway Killer" because he would dump his victims along Southern California roadsides.

He was executed at San Quentin State Prison by lethal injection on February 23, 1996.

Last words: "I would suggest that when a person has a thought of doing anything serious against the law, that before they did that they should go to a quiet place and think about it seriously."

George Bernard Harris

After winning US$500 on a craps game in Kansas on March 11, 1989, George Bernard Harris exchanged the money for two machine guns, then enlisted a second man to hold the guns for safekeeping.

The second man gave the weapons to a third man to hang on to but when Harris wanted the guns back later that night, the third man couldn't find them, and Harris shot him dead with a revolver.

He was executed by lethal injection on September 13, 2000.

Last words: "Somebody needs to kill my trial attorney."

Ted Bundy

Bundy was one of America's best known serial killers but nobody is really sure how many he killed.

He was convicted for killing two Florida State University sorority sisters in January 1978, and a 12-year-old girl three weeks later.

He carried out all three killings after having escaped from jail in Colorado, where he was facing charges in the 1975 murder of a nurse.

He confessed to 30 murders before being executed in Florida's electric chair on January 24, 1989.

Last words: "I'd like you to give my love to my family and friends."

Aileen Wuornos

Aileen Wuornos was a sex worker along Florida's highways who shot several men between 1989 and 1990.

She was convicted of six murders and sentenced to death and her murderous rampage was made into a hit Hollywood movie starring Charlize Theron.

Wuornos was executed by lethal injection on October 9, 2002.

Last words: "I'd just like to say I'm sailing with the rock, and I'll be back, like Independence Day, with Jesus, June 6th. Like the movie, big mothership and all. I'll be back."

John Wayne Gacy

Serial killer Gacy's alter ego was Pogo the Clown and he was hired for countless children's parties and charity events around Chicago in the 1970s.

Gacy was convicted of murdering at least 33 teen boys and young men between 1972 and 1978.

All were killed in his suburban ranch house, most of them strangled or asphyxiated and Gacy buried 26 of the bodies underneath his home.

He was executed by lethal injection on May 10, 1994.

Last words: "Kiss my ass."

Westley Allen Dodd

Convicted serial child molester Westley Allen Dodd pleaded guilty to the 1989 sexual assault and murder in Washington state of two brothers aged 10 and 11 and the kidnap and murder of a 4-year-old boy in Oregon.

He was executed by hanging on January 5, 1993.

Last words: "I was once asked by somebody, I don't remember who, if there was any way sex offenders could be stopped. I said no. I was wrong."

Kimberly McCarthy

McCarthy went to the home of a 71-year-old neighbour in Lancaster, Texas under the pretence of borrowing some sugar before stabbing her to death.

She was accused of killing two other elderly women in 1998 but never faced trial.

McCarthy was killed by lethal injection on June 26, 2013.

Last words: "This is not a loss, this is a win. You know where I am going. I am going home to be with Jesus. Keep the faith. I love y'all. Thank you, chaplain."

Rosendo Rodrigues III

Rodriguez III confessed to killing a 16-year-old girl in 2004 and dumping her body in a Texas landfill.

He was later convicted of killing and dumping a 29-year-old woman in the same manner the following year and was linked to at least five other sexual assaults.

Rodriguez was executed by lethal injection on March 27, 2018.

Last words: "I have fought the good fight, I have run the good race. Warden, I'm ready to join my father."