Authorities need to quickly determine whether a string of New Year's Eve sexual assaults and robberies in Cologne blamed largely on foreigners may be linked to similar offenses in other cities, Germany's justice minister said in comments published Sunday. Authorities and witnesses say the attackers were among about 1,000 men gathered at Cologne's central train station, some of whom broke off into small groups that groped and robbed women. If such a horde gathers in order to commit crimes, that appears in some form to be planned," Justice Minister Heiko Maas told the newspaper Bild. Police in Hamburg are also investigating similar sexual assaults and thefts in the St. Pauli district, which occurred on a smaller scale in the northern city on New Year's Eve. Authorities in Sweden and Finland are also investigating similar incidents in their countries. Cologne police are investigating 379 criminal complaints filed with them, about 40 percent of which involve allegations of sexual offenses. So far, of 31 suspects detained by police for questioning, 18 were asylum seekers but there were also two Germans, an American and others, and none of them were accused specifically of committing sexual assaults.