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In May 1862, Lockman was ordered to join Major General Thomas Hindman, commander of the Trans-Mississippi District. By August 1862, Lockman had been promoted to major and was serving as Hindman’s assistant chief of ordinance. He served as chief of ordnance of Hindman’s First Corps from September 1862 to January 1863.
He was paroled in 1865 and was shot in Galveston, Texas, on January 11, 1869. Lockman died the following day. His murderer, Leroy Cotton, was tried, convicted and sentenced to death, but he committed suicide on the morning of his execution in April 1870.