At this site - http://www.sos.mo.gov/archives/provost/results.asp?txtName=Ripley,&radSearch=ALL&txtKeyword=&selCounty=All
there's an April 9, 1864 listing for Thaddus A. Ripley. There's also a May 5, 1864 entry listing a Mr. Ripley who might be planning an escape from Gratiot Street Prison.
You may want to check the Missouri Union Provost Marshal Papers: 1861-1866, Reel F 1391, at the Missouri State Archives in Jefferson City for more information.