As he sometimes does on quiet afternoons, Robert Dress, 36, took his 9-month-old son, James, on Tuesday to watch the helicopters taking off from the public heliport on 34th Street, near the East River.
At first, it seemed like any other small bonding moment between a father and a son. Mr. Dress, an animator who lives nearby, in Kips Bay, sat on a bench. James was next to him in a stroller. A helicopter was on the landing pad. Its rotors were spinning, causing ripples on the water. As the helicopter lifted off, Mr. Dress told little James, "Look - there it goes."
Then it came back.
"It was already going up," Mr. Dress recalled, "when it spun around a couple of times and flipped over with the propeller underwater and the nose facing Queens." It almost looked like a whale, he said, breaking from the surface and slowly lurching over.
"There was no reaction time at all; the thing went up and just came down," he said. "It's a tragedy."
The accident, in which one passenger died and three other passengers and the pilot survived, turned a section of the extreme East Side of Manhattan into a swirl of flashing lights, screaming sirens and emergency vehicles from mid-afternoon until well after dark.
Mr. Dress said that as soon as the helicopter hit the water, he ran pushing James in his stroller toward a railing. He was shouting: "There's a helicopter down! A helicopter's down! Someone call 911!"
Eventually, he did it himself and stood at the railing, scanning the river for any sign of movement. A minute went by, he said, and there was nothing but the current. Then, at a distance of 50 yards, two men - "They looked like executives," he said - popped above the water and grabbed the helicopter's skids. "It almost looked like they were shipwrecked," Mr. Dress said.
Only minutes had passed, but the authorities had started to arrive. Mr. Dress described a huge response, with squad cars, fire engines, vehicles from the Office of Emergency Management and Police Department helicopters. He recalled seeing a police diver hurry by.
"His wet suit wasn't even on yet," Mr. Dress said, "and he was running toward the water trying to zip it up. Then he just jumped in. That guy, whoever he was, is a hero."
One of the first officials to arrive was Francis McCarton, the deputy commissioner for operations for the Emergency Management Office, who was driving north with two aides on the Franklin D. Roosevelt Drive. He used his emergency radio to contact the Police Department to confirm the crash, and he and his aides got life preservers from the heliport staff and threw them to the men in the water just before police officers arrived.
"I walked out on the helipad, and I saw two guys holding on to the helicopter skids," Mr. McCarton said. He said they were shouting, "We need help - there are three other people onboard."
There happened to be a four-member Hercules Team, a police counterterrorism unit, conducting an exercise nearby. The team members, led by Lt. Larry Serras, arrived at the heliport, climbed a metal railing and jumped into the river.
"We were geared up tactically with heavy weapons," Lieutenant Serras said, "which of course we shed before we went in the water."
The current was stiff, Lieutenant Serras said, and it required hard swimming to reach the place where the downed helicopter had gone under. There, the officers found the pilot and two passengers treading water. The pilot said there was another woman still inside the helicopter.
More police divers arrived. One of them, Officer Jason Gregory, later described descending into the water and finding the woman in the front seat of the helicopter, which had violently struck bottom and was mired in mud.
Back on shore, Mr. Dress worried that he and his son were in the way. They left.
The last thing he remembered was looking over his shoulder as a diver hauled a woman from the water - her cocked head cradled in a wet, rubber arm.