The 18th January 2017 an avalanche destroyed the Rigopiano Hotel and SPA with 40 people caught and a death toll of 29 victims. Some of the authors were appointed as avalanche experts supporting the public prosecutors conducting criminal proceedings on the disaster. This paper describes the general meteorological scenario which produced such event and how field investigations were conducted and other multidisciplinary specialized geologic and engineering forensic techniques (aerial photo interpretation, dendrochronology, photogrammetry, geodesy, snow mechanics, structural engineering) were applied to provide insight on the avalanche dynamics and its interaction with the building. Detailed terrain features and damage evidences will be discussed allowing preliminary considerations on the avalanche frequency, its magnitude and dynamic.