This PhD project addresses one of the major open questions in astroparticle physics: the origin of the astrophysical neutrinos detected at TeV–PeV energies. It will develop a multi-messenger framework to investigate whether gamma-ray active galaxies, especially blazars, are credible neutrino emitters, building on the PhD work of Dr. Enzo Oukacha. The project will combine Fermi-LAT catalogues and light curves, IceCube public event lists, and, when available, selected KM3NeT samples. It will pursue both a statistical approach, based on weighted neutrino–blazar association studies, and a follow-up approach aimed at identifying the most promising targets for H.E.S.S. observations. A central objective will be to combine neutrino-side event information with source-side astrophysical properties in order to construct a more selective and physically informed ranking of candidate associations. The project will rely on advanced data-analysis and machine-learning methods, anomaly detection, and comparison with control or randomized samples.