/usr/share/doc/libinsighttoolkit3-dev/changelog.Debian.gz is in libinsighttoolkit3-dev 3.20.1+git20120521-5.
This file is owned by root:root, with mode 0o777.
It is a symlink to /usr/share/doc/libinsighttoolkit3-dev/../libinsighttoolkit3.20/changelog.Debian.gz