Again updating and correcting query in keeping with documented data I have discovered. Union Army Prisoner of War Records indicate that Henry Brigman/Bridgman was captured by Union Forces in Cheraw SC on March 6, 1865. He served out the remainder of the Civil War at Hart's Island Prison, New York. Comparison of additional dates and locations within the Civil War Records of Henry Brigman, Co.D, 26th Infantry would indicate that he could not have been present at Petersburg and could not have witnessed the death of his brother William.
Source of Information: SC Civil War Records, Microfilm Collection, SC State Archives Publications ,Spartanburg Public Library, Spartanburg,SC