The spokesman for Waiblingen police said they found no trace of the message announcing the 17-year-old's intentions to carry out Wednesday's massacre on his computer. The discussion forum involved has also said that the message never existed.
Heribert Rech, interior minister of Baden-Württemberg, read the internet message aloud at a press conference earlier on Thursday.
"Shit, I've had enough, I am sick of this crappy life," Tim Kretschmer allegedly wrote in a chat room only hours before he went to his old school and shot dead nine students and three teachers. "I might get out alive, but you will certainly hear about me tomorrow. Remember the name Winnenden."
The remarks, said to be part of a conversation with another 17-year-old from Bavaria who told his father about it after the shooting, were made at 2:45 am, said Rech.
Less than seven hours later, at around 9:30 am, Kretschmer entered the school in Winnenden near Stuttgart, armed with a handgun taken from his father's bedroom and more than 200 rounds of ammunition.
He eventually shot dead 15 people and died himself after a manhunt ended in a shootout. State police chief Erwin Hetger said he had turned the gun on himself.
German authorities are now working with the US internet company that hosts the online forum's servers to find out whether Kretschmer made the threat beforehand or not.