Police commander Martin Kirchler said there were still no leads on who the attackers were, according to the Krone newspaper.
Police said suspects had been described as being of North African or Eastern descent. One of them had a broken tooth. Investigators believe the same group was responsible for numerous incidents.
Suspects are a group of five to six men who encircled women in the city center on the night of December 31 and sexually assaulted them. The victims were from Austria, Germany and Switzerland.
Similar attacks occurred in Vienna where three women were harassed, with four more women coming forward in Salzburg. This year’s events were reminiscent of what happened in the German city of Cologne last year when hundreds of women said they had been groped and robbed by men of foreign origin on New Year's Eve.