NEW YORK (CNN) -

Two American flags that were taken from the Brooklyn Bridge are now in the United States and are expected to be returned to the New York Police Department Friday, a law enforcement official tells CNN.

The NYPD said they believe a pair of German artists took the flags and replaced them with two white flags late on July 21, the official added.

The white banners were spotted early in the morning on July 22 by construction workers. At the time of the stunt, many New Yorkers wondered whether it represented an act of terrorism or an anti-American statement.

But the artists, Matthias Wermke and Mischa Leinkauf, said the replacement of the American flags with two massive white flags last month was nothing more than an "art project" by the two performance artists meant to deal with "questions of historical legacy and art in the public sphere."

The investigation into the incident is ongoing, and it's still unclear what, if any, charges the artists will face, according to the official.

The artists dubbed the project "White American Flags," saying that "like an empty canvas, White American Flags invites many readings, multiple interpretations and projections."

Wermke and Leinkauf also stressed they "were careful to treat the bridge and the flags with respect and followed the U.S. Flag Code."

"White American Flags" was meant in part as a tribute to the German-born American architect of the Brooklyn Bridge, John August Roebling, who left Germany in 1831 "in search of a better future in the land of freedom and opportunity," the artists' statement said.

As part of the investigation after the switch, intelligence analysts looked into any possible significance of the day that was chosen to see whether that would yield clues. The date turned out to be the 145th anniversary of Roebling's death.

The Brooklyn Bridge opened in 1883 and at that time was the longest suspension bridge, according to the New York City Department of Transportation.