Mosby finally got the Department of Justice post he wanted as Philander Knox ended his term as attorney general. It was not with the trust-busting unit, however, but with the Bureau of Insular and Territorial affairs, where Mosby worked (at a low salary of $2,400/year) under his brother-in-law Charles W. Russell from 1904 to 1910. In 1905 President Roosevelt again sent him to Alabama to troubleshoot allegations of irregularities at the Port of Mobile. Next, he was sent to Oklahoma to investigate charges against U.S. Marshal (and former Rough Rider) Benjamin Colbert. He also secured an indictment of McAlester attorneys George Mansfield, John F. McMurray and Melvin Cornish for misappropriation of Indian Trust funds, but his superior Russell thought the evidence insufficient and ultimately dropped the charges two years later. Meanwhile, Mosby went back to investigate charges of land frauds against Indian minors, and on his return found little to do.