/usr/lib/x86_64-linux-gnu/libbluetooth.so is in libbluetooth-dev 5.43-2+deb9u1.
This file is owned by root:root, with mode 0o777.
It is a symlink to /usr/lib/x86_64-linux-gnu/libbluetooth.so.3.18.14
/usr/lib/x86_64-linux-gnu/libbluetooth.so.3.18.14