FREE now and never miss the top politics stories again. SUBSCRIBE Invalid email Sign up fornow and never miss the top politics stories again. We will use your email address only for sending you newsletters. Please see our Privacy Notice for details of your data protection rights.

On the anniversary of the shocking assaults which took place on the final night in 2015, a German documentary showed behaviour experts reveal in their opinions, the attacks were planned. Professor and historian Jörg Baberowski said research of the violence shows it was a pre-arranged mass attack, in a location chosen so the world would pay attention. The New Year's attacks flummoxed police who failed to stop women being groped and robbed by men carrying translation notes in their pockets so they could threaten the women in their native tongue.

GETTY Attacks against women on the streets of Cologne have been central to migration debate

GETTY On New Year's Eve 2016 police were surrounding central Cologne

You cannot defend your women Jörg Baberowski

Professor Baberowski said the message of the predominantly North African perpetrators was “you cannot defend your women". In their home countries, he said, "the rapists were killed by their own fathers". The Berlin’s Humboldt University scholar said the attacks were planned in Germany to show their lack of violence against criminals was being interpreted as a weakness. The documentary was shown on Western Germany Broadcaster (WDR) on December 30 as police were getting ready to prevent the same thing happening again. Editors of the documentary criticised a tweet by the police on New Year's Day saying: "Exuberant atmosphere, celebrations mostly peaceful."

GETTY Cologne attackers struck because they wanted to make a point - professor suggests

The claim was branded "a lie" as the show said 1,100 reports of crime were registered that evening, 500 for sexual offences. Seattle-based victim Caitlin described the horrific experience she endured as she was groped under her jacket, between her legs, and pulled back by her hair. The woman said she begged two policemen for help after escaping the gang at around 11pm. Women's rights activist Alice Schwarzer said: "The perpetrators have been doing this since 6 pm, but were not put in their place. “They apparently wanted to show the 'sluts' that they should not be on the streets at night." Experts accused the police of the biggest failings.

Cologne: Sex Attacks and Robberies Tue, January 12, 2016 Thirty-one suspects, including 18 asylum seekers, are under investigation over offences including sexual assault and theft in Cologne on New Year's Eve. Far right protestors in Lepzig have rallied against refugees and German chancellor Angela Merkel. Play slideshow Reuters•Getty 1 of 22 Protestors in Lepzig rally after over 100 women were sexually assualted on New Year's Eve

GETTY Professor and historian Jörg Baberowski said attackers pre-planned sex assaults