NEW YORK (CBSNewYork) — A teenage boy died while he was sleeping when an fire swept through a multi-family home in Brooklyn early Wednesday morning.

As workers boarded up what’s left of the multi-family home at 17 Pulaski Street in Bedford-Stuyvesant, relatives tried to comfort the grieving mother of 15-year-old Jacob Weissman, who was sleeping inside when the early morning fire destroyed the building.

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Larry Reilly is Jacob’s grandfather.

“It was accidental. He was in the bedroom … He had the door closed and the air conditioner on. I don’t think he ever knew what hit him,” Reilly told CBS2’s Hazel Sanchez.

The fire started just after 6 o’clock Wednesday morning.

Henry Robertson lives across the street and woke up to neighbors yelling and screaming outside.

“I peeked through the window and noticed that there were flames coming out of the top window of the building,” Robertson said. “People were banging on the doors, trying to make their way into the building. They ultimately were able to force their way in and I guess wake up all the people there.”

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The flames were so intense, they were unable to reach Jacob.

One hundred fire and EMS personnel responded to the scene.

“We were confronted with heavy fire on the third and fourth floor and hallway of this four-story multiple dwelling,” said FDNY Deputy Assistant Chief Joseph Ferrante.

Firefighters say they discovered Jacob’s body so badly burned, he was almost unrecognizable.

Reilly says Jacob’s mother and two older sisters were out of town and Jacob was home alone.

“He was a great kid. He loved life. He was just… salt of the earth … This is like a nightmare,” Reilly said.

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The fire marshal is still investigating the cause of the fire.