The day had been mostly quiet, except for the thunder of police helicopters and the boom of reggae music coming from the colorful floats of the annual West Indian American Day Parade.

But not long after the official festivities ended, sirens started sounding and violence descended on pockets of Crown Heights, on and around the route off Eastern Parkway. By early evening, the police said, two men had been fatally stabbed and at least two people had been wounded in gun violence, breaking the tenuous calm in Brooklyn.

By the time the parade began around noon — a leisurely 60 minutes later than scheduled, bringing all of its feathery finery and island tunes — the New York City Police Department had long been visibly in place.

“There’s more of them than there are us,” said Vanada Miller, 58, who came from Queens and watched the parade from a bench on Eastern Parkway, wearing a shimmering silver top and waving a Jamaican flag. “It’s much too much, it takes away from it all. But I understand it.”