Complex sentence: After Guiteau's trial, the revolver was placed in the Smithsonian Institution, some time after which (believed to be around 1900) the revolver disappeared, and has not been seen since.
Split into simpler sentences: After Guiteau's trial, the revolver was placed in the Smithsonian Institution. Some time after (believed to be around 1900) the revolver disappeared, and has not been seen since.