New London - Rumors have swirled for weeks about what the mysterious four-story structure being built on a barge at State Pier could be.

Some say it's a movie set. Others believe it's a floating prison, a Defense Department project, condominiums or office space.

The barge and its secret cargo will soon leave the city. Several people familiar with the project either still do not know all of the details or aren't willing to divulge them.

The state Department of Transportation is responsible for the Admiral Harold E. Shear State Pier, and Logistec USA leases pier space from the DOT as one of two facility operators.

A spokesman for the terminal operator said Turner Construction leased space from Logistec around May to build the structure on the barge, but never told Logistec exactly what it was building. The barge will go to a yard in Maine next week so the structure can be completed, the spokesman added, and the contractor has been "very adamant" about "keeping it under wraps."

Chuck Beck, the transportation maritime manager for the DOT, said the department was not involved in the fiduciary agreement between Logistec and Turner Construction and, as a result, "has little to no details on what was being constructed, why or for whom."

The job superintendent provided by the DOT for Turner Construction did not return calls for comment. The company's vice president for communications said he would find out about the project Friday but did not provide any information by late in the day. The construction company was hired by a client for the work.

Two barges of equal size docked at the pier and container units to make up the building were brought in. No construction took place on the second barge, which is behind the first. Workers have not been there in several weeks.

There were several security guards at the site earlier this month. Three of them said the only thing they were told was to watch the building until it was taken away.

The Coast Guard reviewed the plans, since the construction could affect the stability of an ocean-going barge.

Lt. Jeff Janaro, spokesman for Coast Guard Sector Long Island Sound, said the marine inspector told him he could not discuss the plans "for proprietary reasons." Janaro said it's unusual that the person being regulated would ask the Coast Guard not to disclose information for that reason. The Day has filed a Freedom of Information Act request for the Coast Guard documents.

"Usually the marine inspection business is fairly routine," Janaro said. "This is a little outside of the normal realm."

Both the state and federal Occupational Safety and Health Administration offices said they were not involved.

Brian Thompson, director of the Office of Long Island Sound Programs for the state Department of Energy and Environmental Protection, said the department would not require a structures, dredging and fill permit if nothing was built permanently in or adjacent to the water. There is nothing on file in the office, he added.

"It's just a modification on that barge, and we wouldn't require a permit for that," Thompson said.

Tammy Daugherty, the city's director of development and planning, directed all questions about the matter to Logistec and the state.

When asked if the city was told what the building is, she said, "I need to just remain silent. We have not been told. I think it's a security thing. I don't know. We don't have any information on it."

U.S. Rep. Joe Courtney's office was told the building is a movie set. John Johnson, chairman of Operation Sail 2012 and the recent Connecticut Schooner Festival, said he heard the same thing. "I believe I'm right about that, based on everything I've heard over two or three months," Johnson said Friday.

George Norfleet, director of the Connecticut Office of Film, Television and Digital Media, said he was not notified about any film set construction at State Pier, but said he probably would not be if the company is not filming at the site and therefore not applying for a tax credit.

Others speculated the Department of Defense or the New York City Department of Correction is involved.

A Defense Department spokesman said he could not try to figure it out without first knowing which of the many agencies that fall within the department could have paid for the construction.

New York City has a prison barge with cells that was built to reduce overcrowding. The Vernon C. Bain Center in the Bronx is part of the Rikers Island prison.

Sailfest Executive Director Barbara J. Neff said people were calling her office to ask about the building, so she called the DOT. She said she was told the building will be used in New York. "It seems like it's a pretty hush-hush thing," she said.

Most people who were asked said they were curious about it, but for now it remains a mystery.

j.mcdermott@theday.com