How did Social Security know he was alive?

From what I understand, he was hired as a manager at a radio station in Galveston, Texas where he had fled to. He lived there for a decade as Tim Kingsbury using a fake SS number. For some reason, an employee at the radio station did a check on him and found out that he was using what appeared to be forged documents. A search revealed a fake Wisconsin birth certificate and blank Social Security cards with press-on lettering sheets. He was charged with fraud and forgery and was ordered to reveal his true identity to the Social Security Administration. It was at that point the SSA did a check and found out his children in Ohio had received survivor benefits and insurance benefits due to the "death" of Patrick Welsh. That is when they contacted Elizabeth Welsh demanding that the benefits be paid back since he clearly had never died.