Though the convicted murderer is incarcerated for just one death and has since withdrawn his other confessions, police still believe he is a serial killer and one of the worst in the state's history. 

Piers Morgan headed to the sunshine state to speak with Mark about his criminal past and has admitted their short conversation was one of the “most difficult” interviews he has ever done. 

Speaking to Express.co.uk, the Good Morning Britain host revealed that he had been issued a warning ahead of his time with Mark. 

“The detective warned me, he’s going to try and manipulate you, he’s going to try and make you think he is a good guy,” Piers divulged. “Try and make you believe him.

“Like all serial killers, the reason they get away with doing it for so long is because they’re smart. 

“They’re street smart, they’re cunning, they’re manipulative. And he was all those things, he tried to charm me, he tried to make out he was a nice romantic guy and he treated women well.”

The 52-year-old added: “I’m looking at this guy and thinking, I’ve read the details of what you did to these women and you are a horrific human being.”

As Piers investigated the case and met with the families of Mark’s victims, he confessed he was shocked by the spontaneity of his decision to kill. 

“It could be any one of you at any time,” he said. “You’re in a convenience store at midnight picking up a bottle of milk or walking down a dimly lit street. 

“Any one of you from any ethnicity, from any religion, any background, any education. There was no rhyme or reason. 

“It was completely random, you just had to basically fit the bill of being vulnerable to him, a vulnerable woman he could snatch.”

The father-of-four concluded: “That was the most chilling thing about this. That could be any women I knew. The randomness, the spontaneity, the wrong place at the wrong time. It’s horrible. It’s terrifying.”

Serial Killer with Piers Morgan airs tonight on ITV at 9pm.