/usr/share/doc/libbt-dev/changelog.Debian.gz is in libbt-dev 0.70.1-20ubuntu2.
This file is owned by root:root, with mode 0o777.
It is a symlink to /usr/share/doc/libbt-dev/../libbt0/changelog.Debian.gz
/usr/share/doc/libbt-dev/../libbt0/changelog.Debian.gz