German police investigating the Winnenden school shooting, where 15 people died before the killer turned the gun on himself, believe one motive might have been a rebuff from a teenage girl who attended a New Year’s Eve party at his home.

The girl was one of his first victims.

According to detectives, Tim Kretschmer, 17, had a “casual friendship” with the girl, who lived nearby. But she rejected his advances at the party and later ended their relationship.

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The name of the girl has not been released, but it emerged that three of his female victims, Chantal Schill and Jana Schober, both 16, and Stefanie Kleisch, 14, had all lived nearby.

Chantal was the first to die, in her seat near the door of classroom 305 at Kretschmer’s old school. Police said it resembled an “execution." He then shot Jana and Kristina Strobel, 16, and left the classroom, going on to kill Kleisch and four other girls, a boy and three teachers. Three other people were murdered later.

Detectives said Saturday that Kretschmer, who was described by friends and family as quiet and polite, had a secret identity on the internet, where he participated in a discussion about school shootings under the name “JawsPredator1."

“The funny thing is that even when people like that announce what they are about to do in advance, no one believes it,” he was said to have written in an online chatroom. Detectives searching for clues to his character found more than 200 pornographic images on his computer’s hard disk, including 120 photographs of female bondage.

Click here to read more on this story from The Sunday Times.