I believe the individual you are looking for is Nelson Bowman Sweitzer, 1829-98. He was graduated from West Point in 1853, finishing 24th in a class of 52. He was captain of the 1st US Dragoons/Cavalry before the Civil War. During the Civil War he was an aide-de-camp to General Geo. McClellan. One of his claims to fame is that he commanded the regiment that tracked down and killed John Wilkes Booth and captured Dr. Mudd. He received his brevet appointment to Brigadier General after the war. This information comes from the Civil War Dictionary, by Mark Mayo Boatner. He is in a group picture with General McClellan in the posthumously published "McClellan's Own Story." 1887.
What I have not been able to find out is whether or not Nelson Bowman Sweitzer is the brother of Jacob Bowman Sweitzer, who commanded the 62d Pennsylvania Volunteers and later 2d Brigade of the First Division of the 5th Army. Jacob Bowman Sweitzer was 8 years older than Nelson. Jacob was born in Brownsville, Fayette County, PA, south of Pittsburgh.It is possible that Jacob's mother was Elizabeth Bowman, but that is mostly speculation.