DNA clue to Brooklyn Bridge flag gag

STORY HIGHLIGHTS

(CNN) -- New York police have collected DNA evidence in the case of nighttime acrobats who replaced two American flags atop of the Brooklyn Bridge with two white flags, according to a law enforcement official with knowledge of the investigation Friday.

The swapped-out bleached flags were spotted by construction workers at 5:30 a.m. Tuesday.

The DNA was taken from tin pans used by the vandals to cover bridge lights, according to the official -- a clever move to elude detection while the flags were raised. The tin shields were held in place with zip ties.

So far there is no match in existing databases where DNA evidence of solved and unsolved crimes are kept, the official added.

Among other leads investigators are following are five nicknames who tipsters suggest might be associated with the incident. Investigators are trying to learn the real identities behind the nicknames or street names. It's too soon to know whether any of them were involved, the official said.

The motive is unclear: Was it a stunt, prank or something more sinister?

Officials have said they are looking at whoever had access or familiarity with the bridge, including maintenance workers or anyone who worked on the fireworks extravaganza over the East River on Independence Day. The event this year included pyrotechnics shooting from the bridge.

Cell phone calls are being tracked and about 18,000 license tags were checked from vehicles that crossed the bridge in the overnight hours, according to the official.

More than 120,000 vehicles, 4,000 pedestrians and 3,100 bicyclists cross the Brooklyn Bridge every day, according to the city Department of Transportation, which maintains the bridge.

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DNA clue to Brooklyn Bridge flag gag