DW: Identifying the men who participated in the sexual assaults, harassment and thefts in Cologne on New Year's Eve is proving to be a problem. If you don't know who they are, the chances of arresting them are almost nil, right?

Nikolaos Gazeas: That's true. The chances of convicting even one of the perpetrators are slight.

All the same, what is needed in order to take penal action in these cases of massive sexual assault, even including theft in many cases?

You don't need a lot to initiate preliminary proceedings: a so-called initial suspicion is enough, which means that there must be enough real evidence pointing at a crime. For instance, the prosecutor's office and the police would probably make the assumption if it's clear that one of the people in question was at the crime scene that night.

But what is needed to find someone guilty and convict them is a totally different matter. You have to prove a perpetrator's personal guilt. That's problematic in the case of crimes committed from within groups, and it's particularly problematic in the case of New Year's Eve because everything was so chaotic at Cologne's main train station.

What's the procedure if someone is charged after all?

One would have to prove that this person committed a concrete act, for instance robbing and/or sexually assaulting, say, Mrs Miller. If the defendant doesn't confess, you need other evidence to convict the person. That would be video footage and, above all, witnesses, in particular the woman in question, but perhaps also other people who saw what happened. The witnesses would have to testify that it was precisely this defendant - and not someone else. One must also consider that not only the perpetrators were apparently very drunk on New Year's Eve, and thus quite uninhibited, but that some of the victims and potential witnesses had had a drink, too. So the chances of people clearly remembering a certain person are reduced.

If there's any doubt as to whether the defendant was the perpetrator at all, a judge won't and can't pronounce the defendant guilty. If, once the gathering of evidence is closed, the judge is of the opinion that it's impossible to say with enough certainty that the defendant is the perpetrator, the principle "in dubio pro reo" applies in our constitutional state. The defendant must be acquitted.

Is that fair to the victims?

As sobering as this might be in light of the awful events on New Year's Eve, and as disappointing for the victims: it is and remains to be right to acquit a defendant in case of doubt, no matter what the charges were. Even in cases like these, we should not breach this iron-clad fundamental principle of a constitutional state. In such cases in particular, the constitutional state must assert itself and not give in to the temptation of straying from its own principles.

The alleged perpetrators appear to have a migrant background, whether they are recognized refugees, asylum-seekers, tolerated foreigners or people who've lived in this country for a while, some perhaps even with a German passport. What role does a person's status play in case of a prosecution or conviction?

Their status has no direct bearing on either the prosecution or conviction. Everyone is equal before the law, and is treated the same. A status concerning residency or immigration laws would be relevant once a person hasn't only been identified but also effectively convicted. In that case, a conviction could possibly have consequences linked to immigration laws. In case of grave crimes, a person can be deported.

Which groups can be deported?

The question remains whether refugees were among the perpetrators at all. We can't make any such claims without significant evidence. But from a legal point of view, Germany wouldn't be able to simply deport refugees who have been granted asylum but were involved in the Cologne events and who would face inhuman treatment, including persecution, in their native country if they were deported. That would come into conflict with our basic law and international law.

Do you see any reason to amend legislation in the wake of the incidents in Cologne?

No. German criminal law offers sufficient protection against such acts. The crimes we're looking at here involve considerable prison sentences, both for theft and the sexual harassment. Concerning the sex crimes, however, there's the problem that groping a breast, a butt or underneath a skirt isn't immediately punishable as a sex crime. Here, the law requires sex crimes of great relevance. Every case needs to be screened individually to determine when that point has been reached. There have been widely differing rulings on such cases. In some of the cases in Cologne, which apparently saw massive assaults, I would think the level of relevance has been exceeded, which would result in significant prison sentences.

The perpetrators would face significant punishment if they were caught and there was evidence for what they did. Unfortunately, however, chances are slim. In this respect, and to avoid being disappointed, one shouldn't expect too much from the judiciary in this case.

Dr. Nikolaos Gazeas is a criminal lawyer based in Cologne and a research associate at Cologne University.