Was it someone's concept of art or an attempt to send a political message?
Perhaps, as one police official mused, it was a long-lost relative of the first US flag maker, Betsy Ross, inspired to come up with a latter-day creation: two white flags. Early on Tuesday, the white flags mysteriously replaced the American ones flying atop of the Brooklyn Bridge.
Whatever was behind the swap, police said there was no sign of a sinister motive such as terrorism. They played down concerns about the security breach that enabled the flag carriers to clamber atop the bridge's two towers and switch the flags.
Police stationed on either side of the East River span are "focused most clearly on areas of the bridge that are critical to its structural integrity", said John Miller, the New York Police Department's deputy commissioner of intelligence.
Nonetheless, the incident embarrassed law-enforcement officials in a city that prides itself on tight security and anti-terrorism measures. Since the September 2001 attacks, thousands of video cameras have kept an eye on city streets. Audio messages in the subways urge riders to be vigilant, telling them: "If you see something, say something."
Other city landmarks have been targets of security breaches, most recently the tower rising at the site of the fallen World Trade Centre buildings. In March, a teenager sneaked to the top of the new building's spire, which reaches a symbolic 1,776 feet (541.3 metres) into the air, a reference to the year of America's declaration of independence. Last year, three parachutists jumped from the building.
Miller and the city's police commissioner, William Bratton, said on Tuesday that they were "not happy" that someone had scaled the bridge towers, adding that they hoped surveillance cameras would help catch the offenders .This much they do know: At 8.30pm on Monday, the US flags were atop each of the towers, which provide the backdrops for countless tourist photos. At 3.10am on Tuesday, video showed four or five people walking on the bridge's pedestrian path. Within the next 30 minutes, the lights that shine on each flag had gone dark.
And when the sun rose, pedestrians, tourists and construction workers doing routine bridge work noticed the white banners flying in the sky.
By midday, the white flags were gone and the American flag with its stars and stripes was back. Miller said the white banners, each measuring 3.5m by 6m, would be studied for clues, along with two large aluminium pans that had been placed over the tower lights to enable the flag-swappers to work in darkness.
Close inspection of the white flags shows the outlines of Old Glory, indicating they were bleached US flags. That enraged Brooklyn borough president Eric Adams who offered a US$5,000 reward for information leading to the perpetrators.
He said white flags, which usually indicate surrender, had no place on the bridge. "The only thing or person who should be surrendering at this time is the person who's responsible for the desecration," Adams said.
Miller said it appeared that a significant amount of planning went into the swap.
"Perhaps they have experience climbing or in construction or in bridge work," he said, noting that someone would have had to scale each tower from the outside, carrying a replacement flag.
Miller said people who climbed the towers usually planned to jump or send a political message, not commit a criminal act. "If there is a message in it," he said, "we don't know what that message is."