Marcy,
Even though I am away from most of my resources, I located a copy of "Guerrilla Warfare in Civil War Missouri,1862" that I wrote and McFarland and Company published in 2004. This book contains the episode I referred to earlier that MAY describe the incident you seek in which your ancestor, Reinhard Bernard Walland, and others involved in helping Missouri slaves to reach freedom in Kansas were captured and hung by some of Quantrill's band. My writing about this incident is on pages 206 and 207 in the chapter about guerrilla actions in northwest Missouri during autumn 1862, and the sources below are what I cited in endnote #40 on page 233 of that book, as also given below.
Specifically, Quantrill's band raided in Kansas just over the Missouri border on 17 and 18 October 1862. First, the bushwhackers passed Little Santa Fe, southwest Jackson County, in Missouri the evening of October 17 and happened upon a wagon train intended to take goods to Santa Fe. The teamsters foolishly neglected to post sentries when they bedded down for the night, and Quantrill's raiders killed about half of them before the remainder ran away and escaped into the darkness. It's been a few years since I wrote that book, but I would guess that the raiders helped themselves to the cargo of the wagons bound for Santa Fe. The mounted guerrillas next raided the village of Shawneetown, also on the Kansas side just a few miles from the Missouri border. The raiders killed two residents in the village, stole many horses, burned much of the town, and rode back into Missouri the morning of 18 October, 1862 with seven men they captured in Shawneetown. After Quantrill's men were back on the Missouri side of the border, they murdered their seven captives by hanging. I don't believe Shawneetown is located in Leavenworth County, Kansas, but other details of this raid make me think this raid fulfills other details you mentioned.
As I recall reading the sources years ago that I cite below (I don't have them here with me), they don't specifically state why the bushwhackers took those seven men back to Missouri, but I would assume they suspected these men of being northern sympathizers, and we cannot rule out that if the guerrillas determined by questioning these prisoners were guilty of "slavestealing" or aiding slaves to escape to freedom in Kansas, they would murder them in such a way to discourage others from doing likewise. Quantrill's men were known to kill "slavestealers" on other occasions during the war.
In John N. Edwards' 1877 book "Noted Guerrillas, or the War in the West," St. Louis: H. W. Brand and Company, 1877, is a pen-and-ink drawing of the seven murdered men, showing one lying on the ground and the other six hanging in trees. I don't have the page number with me at this location. Other sources I used for this episode include:
--US Department of War, "The War of the Rebellion: A Compilation of the Official Records of Union and Confederate Armies, Wash, DC, 1880-1901, vol. 3, pages 347-8;
--"Guerrilla Raid Into Kansas," newspaper St. Louis "Daily Missouri Democrat," 20 October 1862;
--"Kansas Again Invaded," newspaper St. Louis "Daily Missouri Republican," 23 October 1862;
--Albert Castel, "William Clarke Quantrill: His Life and Times," New York: Frederick Fell, Inc., 1962, page 98;
--William Elsey Connelley, "Quantrill and the Border Wars, Cedar Rapids, Iowa: The Torch Press, 1910, reprinted Ottawa, Kansas: Kansas Heritage Press, pp. 274-5;
--Richard S. Brownlee, "Gray Ghosts of the Confederacy, Guerrilla Warfare in the West, 1861-1865," Baton Rouge: Louisiana State University Press, 1958, p. 103;
--William E. Gregg, manuscript "A Little Dab of History Without Embellishment," 1906, Western Historical Manuscripts Collection, University of Missouri Library, Columbia, Missouri, collection number 113, 1906, pp. 36-7.
That's about all I can do for the present. I hope it helps your quest. I cannot prove Mr. Walland was one of the hung men, but that is my best guess.
Bruce