According to Rose Mary Lankford's Encyclopedia of Quantrill's Guerrillas:
Benjamin Potter may have sold some meat to Quantrill's Guerrillas on Aug 19 1863, two days before the Lawrence Massacre.
The next day after Col. Clark killed Benjamin, Sept 6 1863, Benjamin's son, Marion Potter joined Quantrill.
There is a chance Martin Rice leaked the info because in his biography it states he was a Union man. Martin's daughter that married the Tate is supposed to have died in 1869.