Police have arrested a suspect who stole a truck in Brooklyn and then fatally ran over its owner after he tried to chase after the thug, authorities said.

According to investigators, 24-year-old Joshua Colon first stole the truck from outside Phil Dellegrazia’s A&D Iron Works shop on 24th Street in Sunset Park at about 6 a.m. Dellegrazia usually pulls the trucks out in the morning and leaves the keys in the ignition, said Pablo Rodriguez, who works at the iron shop as well.

Dellegrazia, 63, and another worker then took off after him, grabbing a second truck and speeding down the block, Rodriguez said. They then turned the corner onto Fourth Avenue.

“Something wasn’t right,” said Troy Tecau, 69, who saw the violence unfold from across the street. “And this gigantic truck runs down the street, followed closely by the black truck. The guys caught up at the light.”

That’s when Tecau said a man got out and started banging on the suspect’s vehicle, on Fourth Avenue, between 22nd and 23rd streets.

He said the suspect put the vehicle “in gear and it roared. He was trying to kill him.

“I saw him hit the trash can and I saw the body go flying,” he added. “It was chaotic.”

Dellegrazia was pronounced dead at the scene, where Colon ditched the truck and ran, police said.

On Monday afternoon, Dellegrazia’s family had gathered in front of the scene of the accident and inside the iron shop. They declined to talk to reporters. Car parts still lay strewn across the Fourth Avenue where traffic was blocked heading northbound.

Dellegrazia was the happy father of three kids, said Rodriguez, 48, and was always a great man to work for.

“Everybody knows him, he helps everyone,” he said. “All the time he was happy.”

Tecau said Dellegrazia was a staple of the neighborhood.

“That breaks my heart,” he said. “He was a really nice man and a credit to the neighborhood.”

Colon, of Brooklyn, is charged with second-degree murder, robbery and grand larceny, police said.