Authorities in Germany say a suspected gunman killed one person and injured three others at a university in Heidelberg inside a lecture hall on Monday before killing himself.

According to the Associated Press, police said the lone gunman was an 18-year-old German citizen who was a biology student at Heidelberg University.

He had no known police record, officials told the AP.

Shortly before the shooting occurred, the suspect sent a phone message to his father saying that "people will be punished," police said during a press conference Monday.

Police said the motive is unknown, but the suspect was known to have suffered from a psychological illness, the news outlet reported.

The AP reported that the woman killed has been identified as a 23-year-old German.

Those injured in the shooting were two German women and a German-Italian man.

The AP reported that officers found two firearms and about 100 rounds of ammunition next to the suspect's body.