-- The mystery surrounding two white flags that appeared on top of the Brooklyn Bridge today deepened as the New York City Police Department admitted they don't know who committed the security breach or how they accomplished it.
White flags, which are symbols of surrender, flew from poles on the stone supports atop the famed bridge that connects Brooklyn and Manhattan over the East River.
"I'm not particularly happy about the event," said NYPD Commissioner Bill Bratton.
Police officials said this afternoon that they have surveillance video of a group of four or five individuals walking onto the bridge shortly after 3 a.m.
"Those people will be of particular interest in this investigation," said NYPD Deputy Commissioner John Miller, who also oversees intelligence and counter terrorism.
Authorities said that at around 3:30 a.m., the lights that illuminate the U.S. flags on either side of the bridge could be seen flickering and then going out completely. At 5:30 a.m., construction workers noticed that two seemingly-white flags had replaced the American flags, police said.
Bratton said there was a 13-minute gap between the tower lights going out and the white flags going up.
When police investigated the scene, they found that the two American flags had been apparently bleached and large aluminum tins had been tied to cover the lights that illuminate the flags.
"At this time there is no sign of any particular nexus to terrorism or even politics," Miller said. "It could be someone's art project or a statement, but it's not clear what that statement is."
Miller said they are conducting tests on the flag, joking that he was "not sure if this is Betsy Ross' long lost nephew doing extensive work" to make two large flags.
Miller said authorities think the perpetrators may have had some experience "climbing in construction or bridgework" or have previously been up to the flag platforms on the Brooklyn Bridge.
"When [the NYPD's] Emergency Services went up this morning, the gates were still up and locked," he said. "For someone to go around it and go up to the tower and have right size cover to put over the light, there's some indication of pre-operational planning."
The Brooklyn Bridge -- operated by the city's Department of Transportation -- is one of the country's oldest suspension bridges. The span, which was completed in 1883, is also a National Historic Landmark.