On 9 April 2011, a gunman opened fire inside the Ridderhof shopping mall in Alphen aan den Rijn, a town about 33 kilometres southwest of Amsterdam, killing six people and wounding 17 others before fatally shooting himself. One of the wounded later died from their injuries the same day. Including the gunman's own death, the shooting resulted in seven total deaths. It was the deadliest attack in the Netherlands since a 2009 attack on the Dutch royal family, and the deadliest mass shooting carried out by a lone gunman in Dutch history.
The 24-year-old gunman, a local resident and member of a shooting association, drove to the mall shortly before midday carrying a semi-automatic rifle, a pistol, and a revolver, along with several loaded magazines. He first shot and killed a man in the mall's parking area, then fired on two friends near an exterior staircase and a bystander who witnessed the attack, before entering the mall itself. Inside, he fired at shoppers as he moved through the building, fatally shooting an elderly couple, a man in a mobility scooter, and a woman using a mobility scooter, and wounding several more people near a supermarket and in a side hallway. He fired a total of 119 rounds during the attack. After discarding his rifle and one of his handguns, he shot himself with a revolver near a supermarket checkout. Children were among those injured but sustained only mild wounds. The gunman had left a note in his car falsely claiming that explosives had been placed in three malls in the city, prompting evacuations.
The gunman had a documented history of psychiatric problems, including paranoid schizophrenia, and had spent 10 days in a closed psychiatric institution in 2006 following a suicide attempt. He was reportedly fixated on the 1999 Columbine High School massacre: he chose 9 April because it would have been the 30th birthday of Columbine gunman Eric Harris, and began shooting at the same time of day that Harris died by suicide.
Those killed were Ali van Doorn, 91; Frans Deutekom, 80; Margriet ter Haar, 68; Michael Boezaard, 49; Constanze Boezaard-Bierman, 45; and Nadim Youssef, 42, a Syrian poet and journalist who had fled to the Netherlands after surviving an earlier assassination attempt. Dutch officials, including Queen Beatrix and Prime Minister Mark Rutte, publicly responded to the shooting, and several thousand people attended a memorial service at the mall the following day. In the days after the attack, a 17-year-old was arrested after posting threats referencing the shooting on social media, and several other people were arrested for similar posts.
In September 2019, the Supreme Court of the Netherlands ruled that police in Alphen aan den Rijn had been at fault for granting the gunman a firearms licence despite his documented mental illness, and held the police liable for damages suffered by the victims and their relatives. The ruling was followed by a period of stricter enforcement of firearms licensing requirements in the Netherlands.