On 9 April 2011, six people were killed by a gunman who entered the Ridderhof mall in Alphen aan den Rijn, Netherlands,[8] a town approximately 33 kilometres (21 mi) south-west of Amsterdam.

[15] The first victim was a poet and journalist from Syria who had escaped an assassination attempt, only to be killed by Van der Vlis after fleeing from his home country to the Netherlands.

The shooter was 24-year-old Tristan van der Vlis (June 13, 1986 - April 9, 2011) who lived in an apartment complex in Alphen aan den Rijn with his parents.

[18] He had a history of psychological and psychiatric problems, including paranoid schizophrenia; in 2006 he spent 10 days in a closed institution after attempting suicide.

[22] The Netherlands Government Information Service, through a brief statement on Twitter, said Queen Beatrix was "speechless because of the great loss and sadness;"[24] and politicians such as Minister of Security and Justice Ivo Opstelten expressed feelings of shock and tragedy.

[27] On 20 September 2019, the Supreme Court of the Netherlands (Hoge Raad) concluded that the police of Alphen aan den Rijn was at fault for distributing a firearms license to the perpetrator who obviously had a mental illness.