Indeed the John Highley you mention is the brother of William Madison (Buck) Highley. See the following notation from my genealogy records:
"The capture of Highley was also reported in the St. Louis newspapers and here is a recreation from one of them. This account appeared in the St. Louis Union, April 11, 1864

An Expedition Into Illinois

A FIGHT WITH BUSHWHACKERS

THEIR CHIEF KILLED
The following was received this morning at Headquarters
PILOT KNOB, April 8

To General Ewing:

Captain Milks, 3d Cavalry, Missouri State Militia
Stationed at Farmington, Missouri has just returned from Prairie
Du Rocher, Ill., where he was sent with some members of the
Captain's E Company, after some bandits.

He reports a complete success, having had a fight with a
notorious gang of robbers, killed three and wounding several
among them the notorious bushwhacker and guerilla chief,
John Highley, who had long been the terror of this part of
the State."