The 18-year-old gunman who opened fire at Heidelberg University, killing one person and wounding three others before killing himself, had bought three weapons about a week ago in Austria, German police said on Wednesday.
Two of these weapons were seized at the scene, along with around 150 rounds of ammunition.
The third weapon, a rifle, was found by Austrian police in a room that the man, who was not identified by name in line with German privacy rules, had rented during his stay in Austria, Heidelberg police said in a statement.
Police say the German man — who was a biology student at the university — purchased the two weapons used in the attack from a weapons dealer and the third from a private individual, both in Austria.
The precise motive for the attack is still being investigated, but the suspect was known to have suffered from a psychological illness in the past.
"It cannot be ruled out that a mental illness of the suspect could have been the cause of the crime," the police statement said.
Investigators are also following up on indications that the suspect was a previous member of a far-right party, which he is said to have left in 2019, when he was still a minor.
Police identified the slain woman as a 23-year-old German.
Those who suffered minor wounds were two German women, aged 19 and 20, and a 20-year-old German-Italian man.
The shooting sparked a massive police response, with more than 400 officers sent to the scene.
Heidelberg, which hosts one of Germany's best-known universities, is located south of Frankfurt and has about 160,000 residents.