The 17-year-old gunman who went on a rampage at his former school and killed 15 people before taking his own life gave a warning in an Internet chatroom only hours earlier and said he was "sick of this life," officials said Thursday. Suspect Tim K. told others in the chat room he planned to attack his school in Winnenden, said Baden Wuerttemburg state Interior Minister Heribert Rech. Rech said the suspect wrote, "You will hear from me tomorrow, remember the name of a place called Winnenden." In the first indication of a motive in the shooting, Rech said the teenager told others in the German-language chat room that: "Everyone laughs at me, nobody recognizes my potential." "I’m serious. … I have a weapon here," Rech said the youth wrote. "Early tomorrow morning I will go to my former school." Rech said the chat had occurred the night before the attack, but a police official, Erwin Hetger, later said it was in the early morning Wednesday, about six hours before the 9:30 a.m. shooting. The youth ended the chat saying, "No reports to the police now, don’t worry, I’m just baiting you…"