The mobile phone, with which the remarkable transaction was carried out, was able to be traced, and so the investigators discovered Tanis’ location. He was overpowered by an arrest team soon after.
The investigators — after the identity of the attacker was first ascertained — were only able to hunt down an old telephone number for Tanis.
That number did not lead to any useful information concerning his location. Investigations of friends and family also bore no results. Meanwhile, the threat of further attacks by Tanis had increased.
Due to these enormous risks, the police decided to monitor the bank details of the suspect in real time. This is a very exceptional step say Dutch law enforcement officials.
Shortly after the attack, Tanis logged into his bank account with an unknown mobile telephone and transferred money. The transaction was able to be directly linked to the number of a mobile phone, which could then be checked out using special equipment thanks to an urgent authorization from a magistrate.
The phone turned out to be the property of a friend of Tanis’. The digital tracking exercise led to the location where Tanis was staying. Soon after, a team from the Special Intervention Service raided the location and arrested Tanis.
Meanwhile, it has become clearer why the police and public prosecutor have taken the terrorist motive of the attack seriously. In a letter recovered from the getaway car, Tanis not only reported that he acted in the name of Allah, but also greeted his “Muslim brothers”.