Last week, Timothy Lynch, a fast-talking Irishman wearing a hard hat and a tie, charged into a brownstone on Carroll Street in Brooklyn and grabbed a cigar. Every few hours, he went back into the house, emerging with various articles: running shoes, a pile of passports, jewelry.


He was not slowly robbing the owners. Mr. Lynch, the executive director of the Buildings Department’s forensic engineering unit, was repeatedly popping into the building to make sure that bricks were not popping out and new cracks had not formed. Because at 1:10 a.m. on July 2, half of that brownstone’s right sidewall, and a portion of its back, suddenly collapsed into the alley below.


Within hours, the department decided that the building had been mortally wounded, too badly damaged to be saved, and the very next day, the agency began to have it taken down, piece by piece so as not to damage the homes and the school that surround it. Mr. Lynch was trying to ensure that the building would not come crashing down as it was being taken apart, and while he was at it, he gathered up belongings for the people who lived inside.


Until that Monday, 241 Carroll Street was a beautiful and classic piece of an idyllic leafy streetscape, a chocolate-color brownstone, ornamented with an intricately detailed cornice and bright beige window boxes, across the street from a playground. Today, a rattling buzz consumes the street as the house is devoured from the back forward, ripped apart and shredded with chain saws. It is the sound of a slow execution, the undoing in two weeks of what had stood for more than 150 years.


Three families and eight children lived in that building, and yet, nobody was hurt. A wall fell in onto a child’s bunk bed, but that family was out of town for the night. Several tenants were asleep in their beds on the upper floors, but their walls fell outward. The alley where the debris landed would have been bustling had it been a school day, but it was the middle of a summer night.


“You have no idea how lucky these guys were,” Mr. Lynch said.


In the first few hours, small crowds gathered across the street just beyond a tangle of bright yellow caution tape. They watched as a child’s drawing, still tacked to a wall inside the building, fluttered in the wind.


“I heard something last night,” said a man who lived nearby. “But I was on Ambien, so I don’t know.”


“Did they have pets? Are the pets O.K.?” a woman asked.


“I heard on the news they had a cat,” another offered.


Misty, a longhaired ball of gray fluff, remained missing. But the owners’ dog, a Jack Russell-beagle mutt named Darla, was fine.


Their goldfish also have been recovered.


“We got them four years ago at a fair,” said Sisi Schneider, who owned the building and lived there with her husband, Howard, and their children. “So we’re not sure what’s more amazing, that they lived more than a day after the fair, or that they survived the collapse.”


The Schneiders, now staying with friends, bought the brownstone in 2004 for $1.54 million. The building, which Mr. Lynch said dates to the 1840s, was richly detailed, with hammered tin ceilings, refurbished plaster work and nice wood floors. In 2008, the Schneiders put the house on the market briefly for $3.5 million. They were insured.


“Look at how pretty the ceiling was in here,” Mr. Lynch said, standing on the parlor floor last week amid the elegant rubble. “Not for long!”


A few days after the collapse, the inside of the building looked like a tornado had chewed off the side of the house, leaving bits of the ceiling scattered in chunks across the floor. (“When you see me running,” Mr. Lynch instructed a reporter as he handed over a hard hat, “you run.”) Dust, debris and pieces of the wall coated a bunk bed that was scattered with stuffed animals.