Whoever swapped the Brooklyn Bridge's American flags last month for white ones should be criminally charged if they broke the law, Mayor Bill de Blasio said yesterday.

Responding to claims of responsibilities by artists proud of the bridge designer's German roots, de Blasio said: "I am not a law enforcement professional, but from everything I know, that looks like trespassing, and that looks like other types of charges. Again, I'm going to leave it to the NYPD to answer in specific, but if they have violated a law, of course they should be prosecuted."

The NYPD has said it is investigating the claims by the artists, Matthias Wermke and Mischa Leinkauf. The duo gave The New York Times pictures and video of their handiwork -- evidence that appears to buttress their claims of responsibility.

The prank, which the artists said is meant to honor the bridge's German engineer, John Roebling, who died July 22, 1869. The July 22, 2014, prank proved to be a major embarrassment for the NYPD, which has cops patrolling the bridge around the clock.