Losses of nearly $250,000 at the San Francisco Mint had concerned the Treasury,[16] and, in 1866, McCullough sent John Jay Knox, a Treasury employee, on a special investigatory mission.[17] Knox found that informalities in transferring bullion between various officers of that mint had led to inconsistent sets of accounts, but due to the lack of receipts kept, it was not possible to pinpoint who was to blame.[16] In 1869, Knox, by then Deputy Comptroller of the Currency, was sent by McCullough's successor George Boutwell to investigate other Mint facilities, discovering severe irregularities and large government losses at the New York Assay Office.