Arsenal and Cologne have been charged by Uefa over Thursday's incident which saw around 20,000 fans descend on London – and about 10,000 get into the game.
Arsenal have promised to ban any members who are found guilty of selling tickets to Cologne supporters.
In a statement, Cologne, who were given an official allocation of 3000 tickets, said: “Due to the enormous demand for tickets, it would have been sensible, not least for security reasons, to allow more than the allocated five per cent of stadium capacity to the guest fans.
“It was apparent that thousands of people from Cologne would seek to avoid the restrictions and get tickets in every way possible.
"One such way would be through the help of Arsenal supporters, who passed on their tickets to the FC fans. Some as gifts, but some also for horrendous prices.
“And also despite the tremendous experience of both the London security forces and Arsenal as a permanent partaker in European football, the organisers were unfortunately not adequately prepared for the task.
"In our view, the security concept and communication seemed inadequate and the police force too small.
“FC Cologne would like to unmistakably make it clear that there is no excuse or justification for the fact that a group of so-called disturbers threatened, insulted, and even attacked stewards and police officers without cause. We distance ourselves from this explicitly."