Under a Senate resolution 5/6 Dec 1876, the Senate Committee on Privileges and Elections appointed a subcommittee of three members to visit the State of South Carolina: Angus Cameron (WI), Isaac P. Christiancy (MI), and Augustus Summerfield Merrimon (NC). This subcommittee took testimony in Columbia in December and January and produced a three volume report that is the only place where both sides got to tell their story.
There is occasional sharpness between the senators but this did not have a great effect on the report’s quality, as there is no attempt to draw conclusions, but rather to simply record whatever anyone said.
In the first two volumes, 36 witnesses including Dock Adams and M. C. Butler were tirelessly interrogated on the Hamburgh [sic] massacre. Dozens if not hundreds more were interrogated regarding Ellenton and general election fraud and intimidation. The testimony is presented without obvious redaction.
Volume 3 comprises a further hundred depositions regarding Ellenton, as well as reports, affidavits, statistics, papers, press clippings, roster of the Hamburg militia company, and laws such as the 1866 Black Code and state Militia Laws. The three volumes together run some 2500 pages.
This is by far the most important primary source for the Hamburg Massacre. Steve Budiansky’s The Bloody Shirt is the first book making full use of this source.
So where to get it? It’s a part of the US Congressional Serial Set. These particular volumes are referred to as “44th Congress, 2nd Session, Senate Miscellaneous Document #48 South Carolina in 1876” (or the equivalent shorthand version “44th-2nd S.misdoc 48”). I was able to download all three volumes from Google Books. Unfortunately they no longer have it, but search on “South Carolina in 1876” and you may get lucky. They may also be available through Lexis Nexis at a university with an account. Finally, you may be able to track it down in a large, old library that collected the US Congressional Serial Set in the day.