According to info from SPIEGEL and “Standard”, the Munich shooter had been seen by the authorities in Austria as a possible supporter of the militant Islamist militia HTS. Evidently, a pc recreation supplied clues.
https://www.spiegel.de/panorama/justiz/muenchen-emrah-i-war-behoerden-als-moeglicher-sympathisant-von-al-quaida-naher-gruppierung-aufgefallen-a-0605d6b7-753e-46e2-a9ad-6e86237ac933#ref=rss