Around their neighborhood and their children's expensive school, there was no sign anything was wrong with the Wang family.
The only indication of a problem came in a letter the family sent to relatives in Taiwan describing financial troubles and wishing a final goodbye. By the time the letter arrived, the Wangs were dead.
Police and the city's medical examiner said on Friday that Fred and Christine Wang committed suicide and killed their two children by setting a smoldering fire in their Morningside Heights home.
Toxicology tests determined that all four died of carbon monoxide poisoning, said Ellen Borakove, spokeswoman for the medical examiner.
Drapes had been pulled closed and a blanket placed over a bedroom door, police said. Charcoal was burning in half a dozen pots and bowls. Wang was on the floor, with his wife and children on a mattress nearby, all dead, possibly for days.
Wang, 42, was up-to-date on his steep payments at the children's school, where tuition is US$25,000 per child, said Principal Virginia Connor.
And Connor, who knew each victim -- Wang, his 42-year-old wife, their 11-year-old son, Dennis and 8-year-old daughter, Serena -- said none of them betrayed "any signs of trouble at home."
"This is a small school," she said. "These are two of our cherished students. We have very close relations with every student and parent. To lose four people at once is cataclysmic."
The school was closed on Friday, the morning after a worried relative found the four bodies in a bedroom of the Wangs' apartment near Columbia University. There was no note left at the scene.
Police said a cousin from New Jersey who found the bodies on Thursday night was alerted by other family members in Taiwan who received a letter from Christine Wang despairing about a failed business venture. The letter had apparently wished the relatives goodbye, but police had not seen the letter by Friday evening and did not definitively describe it as a suicide note.
Outside the Wangs' home on Friday, several other residents in the 900-unit apartment complex said anyone in trouble could get help from neighbors.
"I feel bad if they felt isolated," said one neighbor Anne Dixon. "We have a strong sense of community and it's an easy place for children and parents to meet other families."
Richard Braverman, 52, said, "In five years I haven't heard of anything like this here. It's especially heartbreaking when you hear it's children."
Connor, the school principal, said the Wang children had been attending the school since they turned two. Their parents, she said, planned the school's Chinese New Year celebration every year, and were "very supportive of our programs and connected to the community."
Christine Wang picked the children up from school every day, Connor said.
The lobby of the school was decorated for Halloween celebrations, a usually happy holiday for the children. This year, Connor said, the day will be marked by a memorial service.