OAKDALE, N.Y. (CBSNewYork) — A once-historic gem on Long Island’s South Shore is being picked apart and damaged by vandals.

Residents near the former Dowling College say once the school went belly-up, historic buildings were not being protected by the new owners, CBS2’s Carolyn Gusoff reported Monday.

Every night, Oakdale residents walk the sprawling land that was once Dowling College, and almost every night they say they discover and repair heartbreaking vandalism.

“It’s disheartening. I feel like I’m gonna cry. The damage inside is beyond what you can imagine,” resident Al Kulfan said.

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Built in 1901, the 110-room mansion named Idle Hour was a Long Island jewel, the summer estate of William Vanderbilt. Years later, it became Dowling College, which went bankrupt. Since then, things have gotten worse on the property.

“It’s sad. Every night when we walk there is more damage, there’s more destruction, more vandalism,” Neighborhood Watch member David Chan said.

(Photo: CBSN New York)

The 25 waterfront acres were sold to Mercury International, a Hong Kong-based company that agreed to protect historic buildings

“The Historical Society is appalled at the damage to our history, the woodworking that is 100 years old, stained glass, things that cannot be replaced,” Oakdale Historical Society president Maryanne Almes said.

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Copper gutters have been stolen, treasured interiors have been ransacked, and fountains have been trashed. The weeds are so unsightly, residents mow, themselves.

“We have found hammers around the property that they have thrown through the windows, that they have broken off doors,” said Michelle Burke of the Oakdale Historical Society.

“They are like a delinquent landlord. It’s horrible they are allowing this to happen,” Chan added.

(Photo: CBSN New York)

Town of Islip Supervisor Angie Carpenter said she is also frustrated by the private company.

“They’re in China, so it’s very difficult,” Carpenter said. “We have been writing violations left and right.”

The town is demanding Mercury install security cameras or pay to have the town install them.

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CBS2’s requests for comment went unanswered.

“They should be responsible as we are responsible as private homeowners to maintain their property,” resident Kate Chan said.

When Mercury bought the property, it promised to maintain a jewel of the community. Years later, residents say they still don’t know what the company plans to do with all the land, but it said it does know the promise has not been kept.

The Suffolk County Police Department said it is reviewing a request by the Town of Islip to maintain a greater presence at the property, by making it a relief point where officers change shifts.

Carolyn Gusoff