Police say that Wei Chu Wu started the fire because of a domestic dispute with the mother of his child.
The woman and child are safe. The person who died Thursday night was someone else in the SoHo building.
Authorities say the suspect fought to keep firefighters out of the burning building at 41 Spring Street, hindering their rescue efforts.
The person who died was unrelated to the dispute, and the charred body found on a third-floor fire escape was so badly burned that responders could not determine the victim's gender.
Flames shot through the roof while smoke billowed through the building, too intense to survive.
Eyewitnesses say 45-year-old Wei Wu, the tenant from apartment 2A, set the fire in the second-floor hallway after a fight with his child's mother.
An off-duty firefighter from Los Angeles, who was dining in the area, spotted the flames and ran over to the building, where he was confronted by the suspect.
The suspect also fought with a police officer and New York City firefighters who were trying to enter the building. The suspect was treated at a hospital for bruises and a police officer was treated for a broken hand.
Wu was taken into custody and later arrested. He is charged with first-degree arson, second-degree murder, attempted assault of a police officer/fireman and resisting arrest.
More than 200 firefighters fought for hours before finally getting the first under control and keeping it from spreading to neighboring buildings.
The woman involved in the disupte and the suspect's child were able to escape the building unharmed.
FDNY Chief of Operations James Esposito said firefighters had to use the rear fire escape and portable ladders because the heavy fire had burned away the stairways.
"We had an extraordinary amount of fire," said Esposito. "The fire encompassed all the walls and all the floors."
Esposito said the fire completely gutted the inside of the building and at least nine people, including seven firefighters, suffered minor injuries. It was declared under control at 9:20 p.m.
"It's essentially destroyed and it's not going to be livable for quite some time," Esposito said of the building.
The American Red Cross said early Friday that it was providing housing for at least two families and would be meeting with several others later in the day to determine their needs.
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