Student kills 1, wounds 3 in shooting at German university

Since the article isn't up to date, here some missing information:

the victim mentioned in the article was a 23 year old woman who succumbed to her injuries

the perpreator was a 18 year old student at the university, German and living in Mannheim

he did not have a firearms license and bought the shotgun not long ago abroad and still had more than 100 shells in his backpack

he did write someone on WhatsApp that "people have to be punished" and also that he wishes for a burial at sea

there are three other victims that have been injured on the leg, back and face

A double-barreled shotgun and a lever action (Marlin?) rifle. Neither of which are illegal in Germany, but under 25-year-olds have to pass a psychiatric evaluation in order to obtain a firearms license, which he didn’t have. And probably couldn’t have gotten as he “was known to have suffered from a psychological illness in the past.”

Also, other sources mention some kind of ‘proof of purchase’ found in his apartment, implying a legal sale. Assuming countries with some kind of reciprocity agreement with Germany would require a purchaser to have a license from their country of residence, something doesn’t add up here.

Most likely explanation is that I’m completely wrong in my assessment.