By Vanessa Gera
WINNENDEN, Germany — German police worked with U.S. authorities Friday to determine if they had fallen victim to an Internet hoax as they investigate a school shooting in southern Germany that killed 15 people.
Tim Kretschmer, 17, gunned down students at his former high school in Winnenden Wednesday before fleeing on foot and by car, killing three more people, and eventually turning a 9-millimeter Beretta pistol on himself.
Investigators said Thursday that Kretschmer had posted his intentions in an Internet chat room only hours beforehand, but they now say they have serious doubts about the authenticity of the posting.
Police spokeswoman Brigitte Wahl said Friday that investigators were working with officials in the United States, where the servers that host the German-language Web site are located, but did not expect to clear up the mystery quickly.
"It could take a while," she said.
Police said they were alerted to the purported Internet threat after the attack, and released a transcript of the chat at a news conference. But later in the day, after the site itself claimed the posting was fraudulent, they searched Kretschmer's computer and found no trace of it in the computer's history, police spokesman Klaus Hinderer said.
Meanwhile, the attack appeared to have triggered copycat threats.
In a town near Duesseldorf, northwest of Winnenden, police said they arrested a 17-year-old student Friday who allegedly told his fellow students he was planning an attack on his high school.
During a search of his home in the town of Ennepetal, police said they found instructions for how to make explosives and a "chemical substance" that could have been used in the process. No further details were immediately available.
In the town of Ilsfeld, northeast of Winnenden near Heilbronn, police sealed off a high school early Friday after learning of a threat posted in an Internet chat room, said police spokesman Roberto Monaci. Authorities found nothing immediately in their search of the school.
And in the northern state of Lower Saxony, police arrested a 21-year-old man near the town of Soltau who threatened in an Internet chat room to kill 16 people at a school. Police spokesman Peter Hoppe said the man turned out to possess no weapons and claimed to have just been having fun. They plan to charge him with disturbing the public peace.
In Winnenden, residents mourned and expressed shock that a bloody rampage could take place in their small and peaceful town.
Teenagers and their parents lit candles and placed flowers at a makeshift memorial on the edge of the school grounds, while Guenther Oettinger, the governor of the surrounding state of Baden-Wuerttemberg, was expected at city hall to sign a condolence book.
Police were also trying to understand more about the motives of Kretschmer, a quiet and withdrawn teen who wore glasses. Authorities and schoolmates described him as an unobtrusive teenager who had friends and never stirred up trouble in school.
Prosecutors say he suffered depression and had been in brief treatment last year but broke it off against doctors' recommendations. Kretschmer's father is a well-off businessman who legally owned 15 weapons and belonged to a gun club where his son regularly turned up for target practice.
He used one of his father's guns to kill nine students and three teachers in the school. He fled when police stormed the school, and killed three more people before eventually turning the gun on himself after a shootout with police.
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Prosecutors are investigating whether charges can be filed against Kretschmer's father, who was required by German law to keep his weapons properly secured.