Very simply put, the 'Pins' where the pro-Union faction of the Cherokee. Over time, all pro-Union Indians were referred to as Pins or Pin Indians. Members of the Cherokee Keetoowah Society identified themselves by a pin or a pair of crossed pins in the lapel of their coats.

Undoubtedly, the actions of Quantrill and many others had a powerful influence on the Kansas troops in particular. Their information was based more on rumors and gossip and exaggerated stories mixed with strong emotions. The "facts" about Quantrill are only a small part of the equation. Phillips reminded his troops of how they had been treated by the Southern Indians and set out to punish them.

The information available to the Confederates was as bad or worse so we can't be absolutely sure whether the story of killing the wounded is true, an exaggeration, or completely false.

To me, the story is believable considering the environment, attitudes, and intentions. The participants had motives -- retaliation, revenge, or desperate acts to end the war and get home to their families. If it is true that the wounded had their throats cut, this would be more characteristic of the Pins than the Kansas troops. The whites usually shot or hanged their enemies.

At the Battle of Pea Ridge, the Confederates accused the Union troops of killing Confederate wounded. The Pins formerly in Drew's Cherokee Regiment (CSA) later claimed they did it and it was preplanned. They claimed they were looking for an opportunity to defect, which they did en masse about three months later.

This is based on conjecture. The only 'fact' I have is that the Confederate reports claimed it happened. Unfortunately, I'm not aware of any other accounts of this event and especially none from the Union perspective.