WINNENDEN, Germany — "You will hear from me tomorrow, remember the name of a place called Winnenden."
Authorities say a 17-year-old left that message in an Internet chat room six hours before he went on a rampage in his former high school and killed 15 people in this southwest German town.
Tim Kretschmer wrote that he was "sick of this life" and planned to storm the school the next day "and really toast them," Baden Wuerttemburg state Interior Minister Heribert Rech told reporters Thursday.
The transcript released by authorities gave the first indication of what might have driven Kretschmer, described by his peers as withdrawn and shy, to carry out a bloodbath on Wednesday before turning a 9 mm Beretta pistol on himself after a shootout with police.
"Everyone laughs at me, nobody recognizes my potential," Kretschmer wrote in the German-language chat with a teen in the neighboring state of Bavaria. The Bavarian teen told his father and then police about the chat when he realized the threat had been real.
Prosecutors said they had taken steps to contact the U.S.-based provider of the site and were further checking the veracity of the posting, although a message on the site Thursday said that "No killing spree was announced here."
"We are completely convinced of the veracity of the post," police spokesman Klaus Hinderer said.
Across Germany Thursday, government buildings lowered their flags to half staff, while schools held moments of silence for the victims. Germany's national soccer league, the Bundesliga, said players would wear black armbands in upcoming games.
Outside the school in Winnenden, students and residents lit candles and laid tulips, roses, handwritten notes and stuffed animals in a memorial.
Fourteen-year-old Kristin Puengel said a friend of hers was among the eight girls killed. Three female teachers and a boy were also shot in the school. Another three men were killed as Kretschmer fled police.
She said that she only knew Kretschmer — who appeared in pictures shown on German television to be a dark-haired teen with glasses — by sight, but that he was not a friend.
"He was somewhat withdrawn, but I would never have thought (he would be capable) of anything like this," Puengel said.
Authorities and friends said that although Kretschmer played table tennis and lifted weights, his main hobbies appeared to be shooting and spending hours on his computer — where investigators said they found pornographic films, violent computer games and a collection of horror and action films that included "Rambo First Blood," "Freddy vs. Jason," and "The Marksman."
Officials said he had been interested in a girl, but that the feelings were apparently never reciprocated.
"It didn't work out," said Ralf Michelfelder, police chief in the nearby town of Waiblingen.
Kretschmer's father was a well-off businessman who legally owned 15 weapons and belonged to a gun club where his son regularly turned up for target practice, Rech said.
"He was well-trained in firing weapons," Rech said of the teen.
The teen, who graduated from Albertville high school with average grades in 2008, underwent several treatment sessions for depression at a psychiatric clinic that fall, said investigator Siegfried Mahler. Afterward, he was prescribed a session of outpatient therapy, which he never began, Mahler said.
Although authorities said he had struggled in school, Kretschmer was studying sales at a vocational school.
Authorities said they found some 60 shell casings in the school and that the number of victims could have been much higher had educators and police not carried out a plan learned in an earlier training program preparing them to respond to such a shooting.
The principal broadcast a secret code known to teachers and students across the public address system warning them that a gunman was in the school. Teachers swiftly locked their classroom doors and ordered students to hit the floor, tipping over their desks in the process to provide extra protection.
When the first police squads arrived minutes later, they immediately stormed the building, under fire from Kretschmer as they came up the stairs before chasing him from the building, said state police president Erwin Hetger.
"We know from previous school shootings that the perpetrators only stop when they run out of ammunition, when they feel threatened by the police, or when they take their own lives," Hetger said.
"This gunman had more than 250 bullets on him when he entered the school," Hetger said.
Eddy reported from Berlin.