Updated 08/23/16 - 5:25 p.m.
CHICAGO (CBS) -- Three children and a man were killed a in an extra-alarm fire early Tuesday in the South Chicago neighborhood, and police said a "person of interest" was being questioned about the blaze, which officials say appeared suspicious.
The fire started around 1:40 a.m. in a three-story apartment building in the 8100 block of South Essex Avenue.
One witness said he tried to get his own ladder to help people trapped on the third floor, but before he knew it, a man jumped from a window with a baby in his arms.
"To see what I saw and the people leaping in the flames, I could never forget it," witness Byron West said.
Authorities later confirmed a 3-month-old girl was taken to Comer Children's Hospital, and was pronounced dead.
Firefighters extinguished the blaze at around 4:30 a.m., and Fire Department Deputy Commissioner Arriel Gray said firefighters found the bodies of two girls and a man hours later during a search of the building once it was safe to go inside. All three were found on the third floor of the building. The girls were found in one apartment, but not together, and the man was found in an adjacent apartment.
Relatives said the the three children who died were sisters; 3-month-old Melanie Watson, 4-year-old Madison Watson, and 7-year-old Shaniya Staples.
The father of the two younger girls, 36-year-old Michael Watson, was taken to Advocate Christ Medical Center in Oak Lawn in critical condition. Relatives and witnesses identified him as the man who jumped out a third-floor window with Melanie in his arms.
Gray said a 45-year-old man also was taken to South Shore Hospital in fair condition.
The Fire Department's Office of Fire Investigations and the Police Bomb and Arson Unit were investigating the cause of the fire. Gray said the fire was "suspicious," but he said he did not know if an accelerant was used, or where the fire started. A source said lighter fluid from a charcoal grill in back of the building might have been used to set the fire.
A woman who lived in the garden-level apartment where the fire started said she believes a man who had been harassing her for $10 intentionally set the fire.
"I closed my door in his face. He began to punch and kick at the door. I went in my room and ignored him, because I'm like, 'Eventually he'll get the picture and he'll leave.' Never did I think that he was intending on setting anything on fire," Latoya Terry said. "I know where he started the fire. He started it on my back porch."
Police confirmed a "person of interest" was being questioned Tuesday morning.
Gray said, when firefighters arrived, the interior and exterior stairwells had been compromised and were impassable, so crews fought the flames from a defensive position.
Approximately 200 firefighters responded to the blaze. Two suffered minor injuries -- a shoulder injury and a hand injury.
The building has a long history of failed inspections. Building owners repeatedly have been cited for non-functioning smoke detectors, rodents, blocked exits, missing lights, and emergency lights that don't work. An inspection last year also was unable to verify smoke detectors in all units, because access was not allowed to most apartments.
Some witnesses said they never heard smoke detectors go off, but Gray said some were working when he was at the building. However, he said he did not know if every apartment had a working smoke detector.
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