A lack of police officers and equipment created a "survival of the fittest" dynamic in which a mob of mostly foreign men physically prevented officers from helping female victims, a police report leaked to Spiegel magazine says.
The report, dated January 4, paints a chaotic picture of the night, in which groups of up to 30 men "of North African or Arab descent" encircle, sexually assault and rob scores of women outside Cologne's main train station in an incident that has shocked Germany.
Police have received more than 100 complaints - three-quarters of them of a sexual nature - including two allegations of rape.
Though officials have said there is no indication the perpetrators are refugees, the report claims that the heavily intoxicated men taunted police citing their status as asylum seekers.
Spiegel's report said that police "had feared deaths," but failed to go into further detail.
The recent wave of crimes in Cologne - mirrored, though to a much smaller extent, in Hamburg, Stuttgart and Frankfurt - has inflamed an ongoing debate about the repercussions of allowing 1.1 million migrants to enter Germany in 2015.
Police confirmed on Thursday that they are now investigating 16 people in connection with the crimes.
No arrests have been made.
It remains unclear whether the attacks were co-ordinated, though police have said they are investigating links to a North African crime ring known to them for the past 18 months.
MPs from across the political spectrum are calling for the perpetrators to be punished to the full extent of the law.
German Justice Minister Heiko Maas said on Thursday that asylum seekers convicted of sexual assault and other crimes will face deportation.
People sentenced to one year or more in prison can be deported under existing laws "irrespective of their origin," Heiko Maas told Funke Media Group.
