VIENNA—A 27-year-old man who stabbed four people with a knife on a German high-speed train apparently attacked his victims “at random” and showed signs of mental illness, authorities said Sunday. Police and investigators told reporters in Neumarkt in der Oberpfalz that the attacker’s intentions were still unclear, but there is no indication currently of a terror motive. Shortly before 9 a.m. on Saturday, police received a call alerting them that a man with a knife was attacking passengers on Intercity Express train 928, which was traveling from Regensburg to Nuremberg in southeastern Germany. Using an 8-centimeter (3.1-inch) folding knife, the suspect first went after a 26-year-old man in the same train car, wounding him in the head. The suspect then attacked a 60-year-old man, who was wounded on his head and torso, and another 60-year-old man, who also was wounded. At that point, the suspect fled to another train car …