Berlin  - A funeral took place Saturday for the first of 15 victims killed three days previously when a teenager went on a shooting spree at his former school in southern Germany.

Several hundred people attended the schoolgirl's funeral in the town of Winnenden, near Stuttgart.

"We can't comprehend the act that brought death upon her," a Catholic priest said during the girl's funeral service.

Many of her classmates, who had witnessed the shooting, were also present. "You are young and are allowed to live on," the priest said, adding, "I wish that some day, joy will return to your lives."

The girl was one of nine pupils and three teachers killed Wednesday, when 17-year-old Tim Kretschmer went on a shooting rampage at his former school. Kretschmer killed three others as he fled the town, before police cornered him and he turned the gun on himself.

In the town of Winnenden, hundreds of mourners gathered at the Albertville secondary school where the shooting had occurred. People added mementos to the growing pile of flowers, cards and letters dedicated to those who lost their lives.

Meanwhile, questions are being asked about the motives that drove Kretschmer. The teenager had been playing violent internet video games the previous night, news magazine Spiegel reported Saturday.

Spiegel magazine also reported that the teen had been occupied with the subject of school shootings for several months, taking part in internet chat forums about previous rampages in the German towns of Erfurt and Emsdetten.

It remains unclear whether Kretschmer had previously undergone psychological treatment, as had initially been reported.

Police reports earlier in the week said the teen had been treated for depression, however his parents reportedly told Focus news magazine their son had never had psychological therapy.

On the other hand, police and lawyers said Saturday the youth had been to a psychiatric clinic on several occasions between April and September 2008.

German daily Bild ran an interview Saturday with the Kretschmer's grandparents. "We still can't believe it," they said, adding that "to us he was a normal, calm boy."

The shooting has reopened the debate on tighter controls for gun ownership, while Bavaria's CSU, a sister party to German Chancellor Angela Merkel's Christian Democrats (CDU), is calling for a ban on violent video games simulating murder scenes. (dpa)