Program for identifying files from unfinished torrent-downloads?

Are there any programs that can help identify files and directories belonging to unfinished bittorrent-downloads? I've made a mess, and I'm unsure of which downloads are finished and which are not. I could obviously use the bt-client, if I still had the torrent-files, but I don't. I'm therefor looking for way to identify *likely* unfinished bt-downloads - doesn't have to be 100% accurate. I've noticed that bt-clients typically create empty-files, as well as leave files with "holes" (blocks of the file with just NULL-characters), so this could perhaps be a good way to find likely candidates. Sadly, I don't know any good Linux-commands for finding files with blocks of NULLs...