Some sources for what I write below are from:
--John N. Edwards, "Noted Guerrillas," 1877, page 302;
--the 1883 National Historic Company's "History of Howard and Chariton Counties, Missouri," pages 538-40;
--"Bushwhacking in Chariton-Six Union Men Killed," "Daily Missouri Republican," St. Louis newspaper on microfilm, 10 January 1865.

I agree with your aunt's assessment that the murder of John Wink took place during 1864 or 1865. Such violence was rare in Chariton County during the early part of the war, but that all changed in late May 1864 with the advent of an unscrupulous, murderous Federal detective called Harry Truman, whose real name was J. W. Terman. Detective Terman convinced Union Major General William Rosecrans, commander of the Department of the Missouri, that he could with a few troops as escort ride into the heart of the southern movement in Missouri--in his opinion this was Boone, Howard, Chariton, and Randolph Counties--and kill southern men who otherwise were "untouchable" because of their wealth and social and political standing in the area. Terman did exactly that, and murdered perhaps as many as two dozen well-known southern men in those four counties over a few days in late May and early June 1864. Since Terman had the blessing of the chief Union commander for Missouri it was difficult to bring him to justice, and, although some weeks later he was tried and convicted of murder, arson, and larceny, Rosecrans in effect pardoned Terman about the time the Union high leadership relieved Rosecrans of his position. Terman served just a few weeks in jail and then was freed in early 1865.

Now, I wrote all that above because it set in effect what some call a "cycle of violence," more common in present time with gang violence in inner cities. It amounts to somebody hurts or kills a man of one side, and his side in turn murders somebody of the other side for vengeance.

It seemed that Terman began his murder raid in Chariton County and some of those he killed lived near Brunswick. The above sources provide many of the names, but not all. Sadly, John Wink's name is not given as one of the murdered in any of the sources I read, including the newspaper articles even of the "Central City and Brunswicker" newspaper published in Brunswick throughout the war.

In middle June 1864 guerrillas evidently of Clifton Holtzclaw's band killed four northern sympathizers near Keytesville in direct retribution for the Terman killing spree. Holtzclaw was a former southern company grade officer, and was not usually identified with such brutality, but some of his subordinate leaders had no such qualms. Kentucky-born James H. Jackson, who hooked up with Holzclaw's band while they were wintering in Texas the winter of 1863-1864, and came back with them to Missouri perhaps for the thrill of such a daring life was likely one of the leaders of the vengeance killing. Jim Jackson had little regard for life and no known Missouri connections. He seemed to enjoy killing, and attracted to himself several other bushwhackers of similar nature who thought Holtzclaw's gentlemanly nature got in the way with what they thought ought to be done. After Jim Jackson broke away from Holtzclaw later in 1864, he made a name for himself in the large number of men that his small band murdered right up to the amnesty program in June 1865 offered by the Federals when he surrendered.

Some guerrillas, perhaps the same ones, committed more retaliatory robberies of northern sympathizing men in Chariton County on 22 and 23 June 1864.

Bill Anderson's bushwhacker band rode through Chariton County on their way to Howard County July 13 through 15 and killed at least one northern man.

Unidentified guerrillas killed three northern men in north Chariton County on July 22.

These guerrilla killings motivated some members of the local Union 35th Enrolled Missouri Militia (EMM) regiment to set out on their own to commit atrocities, perhaps with the intent that if they hurt local southerners badly enough the rate of violence would slow down or even stop. Of course, that did not happen. You asked what Union troops were garrisoned in Brunswick while this was happening. The answer is none, but there were many men of the local 35th EMM who lived nearby and often a few at a time would be activated from their civilian pursuits to active duty for short periods of time to help guard the 35th EMM firearms and protect river traffic on the Missouri River.

That's about as close as I can get to explaining how John Wink, a southern sympathizer, disappeared near Brunswick. There are cases of men who Union soldiers drowned in the Missouri River, and that may very well be how Mr. Wink came to die and his body disappeared.

Sorry I couldn't pin this down for you any better.

Bruce Nichols