Police and justice ministry officials carried out a second search on the home of 24-year-old Tristan van der Vlis, who shot dead six people in a shopping centre on Saturday and then turned a gun on himself.
The officials were looking for books, notes, videos and dvds which could give more information about the youth and his motives for the killing, public prosecution department spokeswoman Kitty Nooy said.
The Telegraaf reports on Tuesday that friends and acquaintances say the youth was obssessed by violent computer games which bear similarities to the shooting on Saturday.
The AD speculates he may have been influenced by his grandmother, thriller writer Jackie Lourens, who wrote a book called Vier minuten voor half acht (Four minutes before half past seven), in which a gunman shoots people at a train station. She died in 1991.
Van der Vlis lived with his father, a teacher, in a modern block of flats close to the Ridderhof shopping centre where Van der Vlis went on the rampage.
Nooy also said that Van der Vlis now appeared not to have been involved in an incident with an air rifle several years ago. That incident led to Van der Vlis being questioned by police.
Meanwhile, an investigation is now under way into how Van der Vlis managed to obtain a gun licence, given his history of psychiatric problems.
Most of the shops in the Ridderhof centre are expected to reopen today.
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