Police say tension had been brewing among the residents who lived in separate rooms of the same apartment.
The accused killer, LiYong Ye, 43, is said to have had ongoing disputes with residents over things as simple as rent, noise, use of Wi-Fi and the shared kitchen.
Prosecutors told a judge during Ye's arraignment that he suspect blamed the family for his living conditions and planned the Wednesday afternoon attack - even going as far as asking a man living the cramped apartment's third room to pick up his son.
That man returned home to the aftermath of the fatal attack.
Zhao Zhao, 43, was killed on Wednesday with a hammer inside the bedroom of the home at 531 52nd St. in Sunset Park, and her two children, a 5-year-old boy and a 3-year-old girl, were left seriously injured.
Prosecutors say the children targeted in the savage attack "have blunt trauma to their heads and they are likely to die."
They have been transferred to Bellevue Hospital, where their conditions remain critical.
Ye was not found to have any mental health issues or substance abuse.
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Police initially believed the victims had been stabbed until realizing a hammer had been used in the brutal attack.
Officials said the victim's husband works in Ohio and returns to visit his family once a month.
Ye has been charged with murder, two counts of attempted murder, two counts of assault and two counts of criminal possession of a weapon. He has no prior criminal charges, officials said.
Man charged in deadly, 'horrific' hammer attack in Brooklyn
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"It's very rare in our community to have this kind of violence," said State Assembly Member Lester Chang. "And back home in China, they're Fukanese. They live in close quarters, close compact quarters so they're used to it. Something had to trigger" for the man to cross "that moral line."
Local leaders say Ye's 9-year-old son watched the gruesome attack unfold.
"The roommate likely got the call from the perpetrator to say come get my son," New York State Senator Iwen Chu said.
Now without their mother, the two young kids are in the hospital with serious wounds.
"We all have to pray for these young kids," said Chang. "These two young kids fighting for their lives. And I can only imagine what the father has to go through."
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