/usr/lib/x86_64-linux-gnu/libspatialindex_c.so.3 is in libspatialindex-c3 1.8.1-2.
This file is owned by root:root, with mode 0o777.
It is a symlink to /usr/lib/x86_64-linux-gnu/libspatialindex_c.so.3.0.0
/usr/lib/x86_64-linux-gnu/libspatialindex_c.so.3.0.0