ArtAID's 16th Anniversary Ground Zero Memorial photo display was installed in a passageway in the World Trade Center subway station on Sept. 11. View Full Caption ArtAID/Facebook

FINANCIAL DISTRICT — A memorial photography display commemorating the 16th anniversary of the Sept. 11 terrorist attacks was snatched from the World Trade Center subway station after a 9/11 conspiracy theorist insulted and threatened the artwork, according to police.

On the morning of the recent anniversary, graphic artist Keith De Cesare took to the station's underground passageway below Church and Fulton streets to put up 31 photographs of New Yorkers paying their respects at Ground Zero taken shortly after 9/11. But when he returned the next day to retrieve the prints, they had all been taken, he said.

"It was so crushing," said De Cesare, who produces graphic designs commemorating 9/11 victims within the organization ArtAID with his wife Adriana, adding that the prints were obviously part of an exhibition and not up for grabs.

"It was such a disappointment that someone would want to remove it, when it was intentionally there...the pieces were marked that they were property of ArtAID. It was clear if you look at it, it wasn't discarded, it wasn't abandoned property."

De Cesare filed a report with police, who said they are investigating the stolen prints as a grand larceny. He estimated that the prints are altogether valued at between $3,500 and $5,000.

The artist said he has no idea who nabbed the commemorative prints — but he discovered after talking to his wife that she had encountered a man from a group of 9/11 conspiracy theorists while they were putting up the installation.

The group of roughly 30 had been gathered at the top of the subway stairs while the De Cesares put up the prints, he said, about 20 feet from the display.

One man, wearing a shirt that said "9/11 Was an Inside Job," approached Adriana and said "What a waste of paper," before adding, "You better keep an eye on that," according to De Cesare and police, who took down the artist's account.

"Certainly there was an antagonism there and a threat," said De Cesare.

"Had I known that, I probably would have taken it down," he said. "I didn't know that threat was made."

The De Cesares detailed the incident on the ArtAID Facebook page, and are asking any witnesses to come forward.

Keith De Cesare started creating graphic designs of angels commemorating the fallen first responders and victims shortly after the tragedy, he explained, and had posted his work at the site along with a banner reading "Never Forget" that was inscribed with the names of victims. Family members of those lost as well as visitors gathered around the artwork in the months following September 2001, he said.

The photos that were displayed in the subway passage were taken during that time, he said, and showed people interacting with his designs at the site.

While he suspects the 9/11 truthers may have been the ones who stole the prints, De Cesare also fears a money-minded thief may have snatched the high-quality prints for their own gain.

"To me, it's just sad — it's sad that a display that was purely about honoring the lives lost on 9/11 and honoring the memorialization, the history which was my work, that's all it was…it bothers me to see if someone might steal it to sell it because the prints were archival, they were museum quality," he said, adding even he had never sold the prints for profit because the work is "too sacred."

The NYPD said the items were reported stolen on Sept. 15 and that the investigation is ongoing.

MTA spokesman Kevin Ortiz said the transportation authority had no knowledge of the incident and referred DNAinfo New York to the NYPD.