The police detective was the arsonist behind January's inferno, which claimed the lives of long-standing residents Viv Hope and Terry Woods.
However, speaking to Inside Soap, McKell explained that Henshall was trying to make amends for a tragic incident from his past when he started the fire.
The actor commented: "Henshall's wife died in a blaze while he was a constable, but the attack was targeting him. Some bad guys tried to take revenge on him for an investigation and Henshall couldn't rescue his wife.
"Because he felt powerless to help, he invested his life in his career and actually became a very good cop in the process."
He continued: "When he set alight Katie's cottage, he only wanted to start a little fire so he could be a hero and she'd need him. However, her mobile phone was switched off and the landline was unplugged because of all the crank calls he'd been making. He didn't intend to kill anyone."
Henshall's behaviour grows increasingly unstable in next week's episodes as Katie (Sammy Winward) discovers the truth about him - leading to a shocking hostage situation.
> Emmerdale star: 'Katie will be terrified'
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