NEW YORK CITY (WPIX) — Behind a six-story apartment building in Brooklyn was a very disturbing scene after a young mother attempted to kill her 4-week-old baby and toddler on Saturday, according to eyewitnesses.

As tragic as the situation was, it could have been worse if not for the quick action and impressive athletics of a neighbor.

Carl Chin’s apartment is in the row of homes behind the building where the tragedy took place. Around 11:20 a.m. Saturday, he was waking up from a nap. 

“I was laying down in bed,” he said. “Within seconds, we hear a thump, like a body just hits the ground. I pick up my house phone, dial 911.”

According to the NYPD, a young mother pushed the air conditioner out of her bedroom window, then threw her newborn out, down two-and-a-half stories to the pavement. She threw her 2-year-old son down as well, police said.  Then, the mother jumped down herself. All three were naked, according to police.

What happened next, according to Chin’s sister-in-law Shandie Harrison, was even more disturbing.

“She took the baby by the leg … and ‘boom boom,'” she said about the young mother.

Harrison counted out the number of times that she said the mother slammed the baby on the cement. Harrison said she wanted to intervene, but couldn’t scale the 8-foot-tall chain-link fence separating her home from where the mother and children were.

Her brother-in-law, however, ran right for the barrier preventing them from intervening.

“He was like Superman and jumped over the fence,” Harrison said.

Chin reached the mother and children, and was able to stop her from bashing the baby a third time, according to witnesses.

“[I] used my forearm and got her to loosen her grip on the baby,” Chin said. 

He was able to calm the mother down until paramedics and police arrived minutes later.

“She’s clearly not in her right state of mind,” he said. “She must’ve had a mental breakdown. She actually thanked me and told me [to] take care of her daughter,” said Chin.

Harrison said understanding for the mother is needed at this time.

“She’s not to be judged … because we all go through depression,” she said.

The newborn was listed in critical condition, and the mother and 2-year-old were reported in stable condition by police.  

New York has a safe haven law, the Abandoned Infant Protection Act, that allows a parent to safely give up a baby up to 30 days old anonymously and without prosecution. Parents can surrender an infant at hospitals, staffed police or fire stations, and other designated spaces. A parent cannot be charged with a crime if the baby is left with an appropriate person or in a suitable location if the parent immediately notifies an appropriate person of the infant’s location. For mental health and suicide prevention resources, click here.