McClellan’s Snipers Target Slaves
The North used slaves for heavy labor on fortifications as did the South; the former would later use them as troops in an attempt to reduce unpopular levies for white Northerners who were reluctant to enlist after the grim reality of casualty reports sunk in.  In contrast, the South would enlist black troops only after attrition had severely reduced their ranks.  The quote at the end of the passage below is odd as McClellan had invaded the State of Virginia under Lincoln’s orders, meaning both had committed treason (as defined by the US Constitution) as did John Brown.  The latter was hung by Virginia authorities.
Bernhard Thuersam, Chairman
North Carolina War Between the States Sesquicentennial Commission
"The Official Website of the North Carolina WBTS Sesquicentennial"
McClellan’s Snipers Target Slaves:
“[McClellan] opened his offensive on April 4 [1862] when both armies clashed for the first time; sporadic contact continued, but Little Mac’s thrust at Richmond degenerated into the siege of Yorktown that lasted until May 3-4, when [General Joseph E.] Johnston decided to break off the stalemate without a fight. [McClellan] decided to do nothing of significance for the next month while his troops and former slaves hauled his heavy guns into place.
While he entrenched, McClellan approved the use of Hiram Berdan’s U.S. Sharpshooters to pummel [General John B.] Magruder’s lines.  The New York-born Berdan, a national rifle champion before the war, was described by one associate as “unscrupulous and totally unfit for command”; yet during much of the siege his handpicked shooters spared no one.
Every time a Confederate trooper moved his head, they were ready with deadly aim. “Dragging their rifles beside them, the distinctive green-clad snipers stealthily took to tall treetops and secluded stone pits just a few hundred yards from the enemy,” writes historian Charles Bryan.  Using cover of darkness, they typically awaited the coming dawn to open fire.  “The astonished Rebels,” Bryan continues, “scattered as Berdan’s boys cut down everyone in sight, including Southern slaves carrying ammunition to the front.”
Berdan was particularly proud of his work, he added, because “the rebels are trying to destroy our country.”
(Prince John Magruder, His Life and Campaigns, Paul D. Casdorph, John Wiley & Sons, 1996, pp. 146-147)