Germany's Federal Criminal Police Office (BKA) announced on Wednesday that is seeking to file criminal charges against whatever individual or group was responsible for the cyber attack that shut down its eyewitness information portal for the Berlin Christmas market attack.

Originally reported by the news consortium Funke-Mediengruppe on December 20, the BKA later confirmed that it had been hit by a denial-of-service attack. This means that hackers block access to an online resource by flooding it with so many requests the system becomes overloaded.

The BKA set up the online portal for eyewitnesses to upload photos and video footage of the attack on the Breitscheidplatz Christmas market which left 12 people dead. The hack occurred over a period of two and a half hours the day after the incident, when authorities were still unsure of the identity of the assailant.

The next day, German police announced that they suspected Tunisian national Anis Amri of having hijacked a Polish delivery truck, killing the driver and carrying out the attack in the German capital. He was shot dead two days later after an altercation with Italian police officers in a suburb of Milan.

While "Islamic State" (IS) terrorists claimed responsibility for the violence in Berlin, no group has claimed the BKA hack.

es/kms (AFP, dpa)