The Morgan Co. Historical Society does have the Newkirk Family Genalogical book and expect that has your grandfather and Peter Thixton's burial at Newkirk Cemetery in Moniteau County, MO. Both of those names were familiar names in Morgan Co. in that era.
We do have individuals interested in cemetery study in Morgan Co., MO, and have the court records for the county now in possession of the museum. If you'd like to call up there on weekdays between 10AM and 4PM, perhaps they can run the search for any information on the trial/testimony on the stolen cattle.
Sorry I couldn't be of assistance on this one.