The man who was known a generation ago as the “Wyandanch railroad rapist” told a Suffolk jury Friday that he couldn’t have beaten his girlfriend to death last year because he was busy stealing and reselling Bluetooth headsets.

Besides, Willie Johnson said, he would never lay a hand on Thelma Stewart, 49.

When she lost control of her bowels in their bed the night of May 12, 2015, Johnson, 60, said he was worried.

“It scared me,” he testified. “I was concerned about my baby.”

Johnson is on trial before Suffolk County Court Judge Barbara Kahn in Riverhead. He is charged with first-degree manslaughter, and faces a maximum of 25 years in prison if convicted.

He already did 18 years behind bars after he was convicted of a series of knifepoint rapes, mostly committed near the Wyandanch train station, in 1979 and 1980. In this case, he is accused of beating Stewart in the Wyandanch room they rented for $309 a month.

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During questioning by his attorney, Donald Mates Jr. of Hauppauge, Johnson conceded that he yelled at Stewart a lot, but only because she was a severe alcoholic who never ate. He wanted her to eat, he said.

“She’d drink from the moment she woke up to when she went to sleep,” Johnson said.

On May 12, Johnson said he bought her some food and instead of doing his usual work as a landscaper, he took a bus to the Big Lot store on Sunrise Highway. Mates asked why.

“To hustle,” Johnson said, and Mates asked what that meant. “I was going to steal out a store.”

“Whoa, wait a minute,” Mates said, and Johnson explained he could make a lot more money stealing Bluetooth headsets than landscaping. So he said he stole “a lot” of them.

When he got home, he said Stewart was bruised and injured, and a neighbor said she fell.

“I go for it, because my girl do fall,” he said. “She bumps into things and stuff.”

But then her condition worsened at night and she lost control in the bed, he said. He called for an ambulance the next morning and was arrested by police.

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During cross-examination, Assistant District Attorney Raphael Pearl noted that Stewart was covered in brusies, had a broken nose, broken jaw and an injured spleen. Pearl said somebody must have been beaten her.

“I know I didn’t,” Johnson replied. “It was probably one of the crackheads who are in and out of the house all day long. It’s like Grand Central station for crack.”

Johnson told Pearl he’d be willing to take a lie-detector test.

“What about that?” Johnson said.

Pearl ignored him.

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Closing arguments in the case are scheduled for Monday.