Sorry for the delay. This has been a busy week.

How sure are you that Walter Huston Gilbert actually died on 9 September 1862? Assuming you are correct, I write the following:

The story actually began when Quantrill's band raided Olathe, Kansas on September 6 and 7, 1862. William Gregg wrote in his memoir that Quantrill led this raid to avenge the Union execution of band member Perry Hoy at Fort Leavenworth earlier. The bushwhackers were very punitive killing eleven men in all, destroying a newspaper office at Olathe, and leaving with wagonloads of plunder including window casements, as I recall my reading. When the band first rode into Olathe they captured a large number of Kansas militia (killed one who resisted) whom they held through the night and released on parole the next morning when the guerrillas returned with booty to the Missouri side of the border. (There are several sources for this raid by Quantrill's band.)

The Union military in the area responded with a punitive raid of their own led by Lieutenant Colonel John T. Burris and elements of three regiments (his own 6th Kansas Cavalry, 8th Kansas Infantry, and 3rd Wisconsin Cavalry) from Fort Leavenworth between September 8 and September 23. The Kansas expedition lumbered around Jackson, Cass, Johnson, and Lafayette Counties for about two weeks only occasionally finding guerrillas who were smart enough and well-mounted enough to generally stay out of Burris' way. The surviving record consists primarily of general narrative mostly devoid of specific actions (Source: "Official Records," series 1, vol. 13, pp. 267-8). Burris reported that in all he killed two Rebels and wounded a number more, burning 12 Rebel houses, and returning to Kansas with 60 captured slaves, 100 horses, 100 firearms, and etc.

Olathe, Kansas is just a few miles west of the Jackson and Cass County line on the Missouri side, so Burris took his Kansas expedition first to north Cass County on September 9 and 10. If you look at a Missouri map you will see that Rose Hill in southwest Johnson County and Holden in west Johnson County are just a few miles north and east of that Cass and Jackson County line. Throughout the war the Rose Hill and Holden neighborhoods of Johnson County were decidedly southern in sympathy, and the Kansas Jayhawker raids had a lot to do with that. I would assume that some part of the Kansas force happened upon your Gilbert ancestor and killed him because they suspected him of being a guerrilla or because they were frustrated at not being able to kill bushwhackers and...well, you get the picture. This is merely conjecture, of course.

There is another possibility, too. The "Official Records" reveals that at this time the 1st Iowa Cavalry Regiment was at this time stationed in the area just to the south of Johnson County. In Broadfoot Publishing Company's large set published just a few years ago "Supplement to the 'O.R.'", part 2, vol. 19, 1st Iowa Cavalry, p. 62, it states that elements of Company C of that regiment stationed at Clinton, county seat of Henry County, fought a skirmish September 9 somewhere on or near Big Creek that at no Union loss resulted in the deaths of three Rebels and the capture of two more. Big Creek flows just a short distance from Rose Hill and a few miles west of Holden. Sometimes in those old Union army reports the unit gave the location of a nearby village, town, creek, or river, even though the actual fight took place some distance away from the named place. This is what the records of the Company C of 1st Iowa Cavalry actually state in the resource I cited:

"Previous to September 20 the company was engaged at Clinton in scouting and doing guard duty. September 9 had a

a skirmish on Big Creek. Killed three and took two prisoners."
Unlike some other Union units operating in Missouri at this time, the 1st Iowa Cavalry mostly played by the rules, so if they state that they "took two prisoners" than they probably did capture two southern men and sent them along to the military prisons in the St. Louis area. I have no other record of this skirmish September 9 at Big Creek other than a mere mention in Frederick Dyer's volume 2 (of three) "A Compendium of the War of the Rebellion" on page 804 which states:

Sept. 9, 1862, skirmish Big Creek, First Iowa Cavalry.
I would assume that Company C sent a patrol toward Big Creek perhaps to lend a hand to Burris' lumbering expedition that was operating in the same area.

There. That's as close to solving your riddle as I can get. I hope it helps.

Bruce Nichols