Winnenden, Germany - Church bells rang out across the south-west German town of Winnenden on Saturday as a memorial service got under way for victims of the school shooting that left 16 dead.

German Chancellor Angela Merkel and President Horst Koehler were among the congregation at the Roman Catholic church of St Karl Borromaeus (Charles Borromeo) where the service was held.

Because there was not enough room in the 900-seat church, the event was relayed to 15 large video screens set up in other churches and sports stadiums in the town. It was was also broadcast live on national television.

Police estimated that up to 100,000 people were in the town for the service, swelling the population to nearly three times its normal level. Some 500 police officers and 900 members of the emergency services were on duty.

Many shops were closed for the day and black ribbons hung from trees and buildings as Winnenden remained traumatized from the tragic events of March 11 when teenager Tim Kretschmer went on a shooting spree at his former school, killing nine pupils and three teachers.

He also shot dead a gardener before commandeering a car and fleeing to the town of Wendlingen, 40 kilometres away, where he gunned down two other people before police caught up with him and he shot himself in the head.

Kretschmer, 17, killed his victims with a Beretta pistol he stole from his father, a hobby marksman who kept 15 weapons at his home and is now under a criminal investigation on suspicion of involuntary manslaughter.

Police have not yet established a motive for the slayings, but links have been drawn to the youth's love of guns and violent computer games as well as the fact that he was suffering from depression.

In open letter to Merkel and Koehler, the families of the victims appealed Saturday for the introduction of laws restricting the access of young people to guns.

"In our pain, in our helplessness and in our anger, we do not wish to remain idle ... (We want) to help so that we will never have another Winnenden."

The message, which appeared in the local newspaper Winnender Zeitung, also called for less violence violence to be shown on television and a ban on extremely violent computer games.

The Albertville Secondary School where the tragedy occurred has remained closed since the fateful day amid discussions on whether it should ever be used again. A sea of flowers and candles adorn the entrance to the grounds.

A dozen candles and a bunch of flowers were place outside the home of Kretschmer during the night, along with a note that police said was apparently written by an acquaintance of the youth.

The family moved out of the detached house in the aftermath of the killings, the worst school shooting in Germany since a teenager killed 16 people and himself in the eastern town of Erfurt in April 2002. (dpa)