/usr/include/fastjet/ is in libfastjettools-dev 3.0.6+dfsg-3build1.
This file is owned by root:root, with mode 0o755.
..
/usr/include/fastjet/tools/
/usr/include/fastjet/tools/BackgroundEstimatorBase.hh
/usr/include/fastjet/tools/Boost.hh
/usr/include/fastjet/tools/CASubJetTagger.hh
/usr/include/fastjet/tools/Filter.hh
/usr/include/fastjet/tools/GridMedianBackgroundEstimator.hh
/usr/include/fastjet/tools/JHTopTagger.hh
/usr/include/fastjet/tools/JetMedianBackgroundEstimator.hh
/usr/include/fastjet/tools/MassDropTagger.hh
/usr/include/fastjet/tools/Pruner.hh
/usr/include/fastjet/tools/RestFrameNSubjettinessTagger.hh
/usr/include/fastjet/tools/Subtractor.hh
/usr/include/fastjet/tools/TopTaggerBase.hh
/usr/include/fastjet/tools/Transformer.hh