I hope someone can come up with more information on this event. This is a very sad story in Britton's 1863 memoirs ( Memoirs of the Rebellion on the Border -- 1863).
Britton's memoirs read very different than his other works such as the Union Indian Brigade and The Civil War on the Border, both of which were written long after the war and draw on other accounts including the Official Records. His memoirs are actually from his journal he kept during the war and gives his views at the time without the many years of reflection, influence of the accounts of others, or the political correctness of the times. It is interesting to me that Britton was an abolitionist and had strong feelings about slavery. He also expresses his interesting perspective of "Southern culture". I highly recommend reading his Memoirs of the Rebellion on the Border -- 1863 for an interesting viewpoint from an eye witness of the Civil War in and around the Indian Territory.
Also, his Pioneer Life in Southwest Missouri is an interesting account of his views and experiences leading up to hostilities in 1861 including a trip to Texas and events along the Kansas-Missouri border.