Pacman has a complete ist of all files which belong to an installed package in its database. In theory it should be easy to look if some files are missing and list the impacted packages. Is there a pacman command that provides such functionality?
1 hour later after intensively digging the web I found that
paccheck --md5sum --quiet
does this job perfectly…
pacman -Qo /usr/bin/paccheck /usr/bin/paccheck is owned by pacutils 0.10.0-1
Thanks, I forgot to mention that here.