A callous killer finally showed remorse for setting a great-grandmother on fire - minutes before he was executed on on Tuesday night.

Matthew Lee Johnson, 49, received a at the state prison as victim Nancy Harris' relatives watched through a window. Johnson had splashed shop assistant Ms Harris, 76, with lighter fluid and set her ablaze 13 years to the day amid a sickening robbery.

Turning to face Ms Harris' three sons, two daughters-in-law and a granddaughter at the jail in , Johnson slowly said: "As I look at each one of you, I can see her on that day... I please ask for your forgiveness. I never meant to hurt her.

"I pray that she’s the first person I see when I open my eyes and I spend eternity with. I made wrong choices, I’ve made wrong decisions, and now I pay the consequences."

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There was little reaction from Ms Harris' family members, who then watched Johnson gasp several times following the injection of the sedative pentobarbital. He was pronounced dead after 26 minutes of the jab.

The criminal was high after smoking $100 (£75) worth of crack cocaine when he targeted the shop in Garland, Dallas, on May 20, 2012. Johnson walked in, poured lighter fluid over Ms Harris, who had worked at the convenience store for more than 10 years, and demanded money.

After Johnson grabbed the money from the register, he set Ms Harris on fire and calmly walked out of the store, according to court documents. Ms Harris frantically tried to extinguish herself and her clothing, exited the store and screamed for help before a police officer used a fire extinguisher to douse the flames covering her body. The mum of four was able to describe the suspect, leading to Johnson's swift arrest, but the pensioner died of her burns days later.

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Johnson’s subsequent execution was the second carried out Tuesday in the United States. Hours earlier in Indiana, .

And , before which he shouted: "President Trump, keep making America great. I’m ready to go."

Johnson, though, was the fourth person put to death this year in Texas, historically the nation’s busiest capital punishment state. His attorneys had argued his death sentence was unconstitutional because he was improperly determined to be a future danger to society, a legal finding that was needed to sentence him to death. His most recent appeals had argued his execution date had been illegally scheduled.