The family of a World War II veteran and US Army Staff sergeant are haunted that the resting place of their beloved father, Thomas Cahalan, has been vandalised four times this year.

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Mr Cahalan (1914-1987) was also a long-time employee of the Upper Lachlan Shire Council.

The plot is in the Catholic section at the Crookwell cemetery.

In April this year, Kim Cahalan visited the plot to prepare it for his son's visit on Anzac Day. His son, who served in the Royal Australian Navy, was carrying a flag at the local services.

The headstone was covered in a black oil-like substance, similar to coffee or treacle. Since April, this malicious damage has happened a further three times.

The police are using every possible resource to investigate, officer-in-charge of Crookwell Inspector Matthew Hinton said.

Two incidents were reported in May and August; however, the family has notified the police of all four occurrences.

"Anything to do with cemeteries and headstones, we take this very, very seriously," Inspector Hinton said.

"We will use any investigative method to make sure this doesn't happen again."

Police describe the substance as non-damaging, but the Cahalans say it has eroded gold lettering from the headstone. Bleach, used for cleaning, left a residue. They also claim that four gold and white angels were removed.

The headstone was carved in 1990, three years after the death of the soldier and a submission to the US Army, which entitled a marker.

"It's very upsetting that my grandkids, who want to see their great-grandfather's grave, might not be able to," Kim Calahan said.

The Cahalans have put in a submission to the Upper Lachlan Shire Council to install a security camera, which would point only at the grave of Thomas Cahalan.

Local police are also working closely with the council.

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