Tracks the user who trashed a post and when they trashed it. Displays that info as columns in admin trashed posts listings.
The visibility of the "Trashed By" and "Trashed On" columns can be controlled by the "Screen Options" slide-down options panel available at the top right of the page when viewing the trash listing in the admin.
The user most recently responsible for trashing a post will be recorded as the trashing user.
This should only be the case for posts that were trashed prior to activating this plugin (or any time when the plugin wasn't active).
No. Once a trashed post is restored and thus removed from the trash, the information about when and who deleted the post is deleted.