The Mudd family, David Herold and the Sothorons.

[John Stanton]

Jim. I don't know any more about Williamson than you do. however, my interpretation of the info may differ from yours. So, here I go.
It appears that Williamson was a "favorite son" in Richmond. He was West Point (W/o a degree). He took assignments willingly and excelled. Early in the war, he helped set up the Spy system on the Potomac. He had a good relationship with R. E. L., Pendleton, Jackson, Beauregard, Ruggles and more.
The Story Line on his assignment to K. G. was "to find Booth".
WHY? The South had been dealing with Booth for some time, and did little to help - as far as we know. Now, vey overtly, they send Williamson to find Booth. What was their motive, Did they want to save Booth, or destroy him? Williamson was qualified to do either.
In Jan. "65, Capt. J.L.Smith, was sent to K.G. to assess the situation in K.G., as it related to the abduction of Lincoln. He, specifically visited Dr. Stuart, and Charles Mason. Stuart you kown about, but Mason, may be new to you. He was State Senator from K.G., and married to Thomas Jefferson's granddaughter. His Brother was Roy Mason, who was the father Enoch Mason. Enoch's sister was married to Gen Charles W. Field. This is a fine collection of large egos, who may have ideas of their own, on how to handle Booth. I think, maybe was sent to make these guys cooperate. (Stuart did not want to help, but for some reason he did a minimum - but he did help. )
This is a small sample of how the Secret Service worked. An agent gave information,r received info from, someone that he knew. (Thomas Jones was related to Thomas Harbin, etc. etc.) ( Thomas Jones did not know to whom he should send Booth - so he sent him to a TREE near a bridge, and told to wait - someone would find him.)
In Summary: Williamson was "trained". Richmond sent him "get Booth", (you decide what that meant). Williamson arrived in K. G. April 19/20, well after Richmond knew of the assassination. Richmond wanted something to happen. WHAT? I don't know. IMO something would have happened if young Enoch found Booth before he did. Booth was moving too fast for Enoch to notify Richmond? Mosby? the Protection Troops? and get back to his Uncle (Charles) for him to contact Williamson. (Or did he?). Thus, Williamson was involved with Booth, but might not have a chance to do "his job".
I guess this is "Historical Fiction" (Good solid facts w/o a conclusion.) I'M READY TO LISTEN TO ANY ANSWERS TO "WHY?")