The Navy veteran who claims Rep. George Santos cheated him out of cash intended for his dying dog’s cancer treatment, says he’ll get justice if the lyin’ congressman is hit with criminal charges.

Richard Osthoff tells TMZ … he views the alleged scam as both wire fraud and charity fraud — calling Santos a swindler because he used an alias to get away with the whole thing.

The vet was joined by NJ Veterans Network President Michael Boll when he told us he’d already tried to bring charges against Santos — but because he was going by Anthony Devolder back then, it led to a dead end.

Osthoff didn’t fully disclose what action he’s taking to now against Santos, but he tells us government agencies are looking into the case.

As we reported, his late pooch, Sapphire, was a beacon of light for him after getting out of the service and becoming homeless. He realized she needed life-saving surgery when a tumor on her stomach grew larger every day.

He claims Santos, or Devolder, told him he ran an animal rescue, and created a GoFundMe campaign that raised enough to cover Sapphire’s surgery — only to have Santos send him to a different vet, who said the tumor was inoperable.

Osthoff had no choice but to watch his pup die … while Santos allegedly made off with the thousands raised Sapphire.

BTW — Santos decided to put a POW-MIA flag in front of his office amid his latest scandal … and Osthoff sees it as a huge disgrace to him and other vets.