Der Spiegel, a German magazine reports that law enforcement identified him as a German citizen with Turkish roots. A search warrant did not provide any evidence. He was found dead two days later in his car in front of his parents home. Foul play was ruled out, likely cause of death might be a heart attack.
Warning, German and behind paywall: https://www.spiegel.de/politik/deutschland/jstark-waffenbastler-ikone-ueber-halle-attentaeter-und-waffen-aus-dem-3d-drucker-a-cb0a3d1b-4173-4b22-a82c-18b6ea9efbb9