Ok, reading the scans of documents on bitcoin-24.com again (german), the legal situation looks a bit more complicated than just one accusation.

Money laundering:
According to the documents the bank where the German account is, Commerzbank, had asked the polish bank about a number of transactions.
These transaction were from german bank accounts that fell for fishing attacks and onto the Commerzbank account. Simon then transfered funds to his polish account.
On March 5th the polish bank answered a request regarding details of these transactions, a full months before the drama started.

On April 9th his polish account was frozen. I couldnt find the actual date when the german account was impounded, but April 9th is before the big market fluctuations and days before bitcoin24 went offline.

As a comment on this, according to European laws on money laundering (which are in effect in Germany) as Simon was operating a currency exchange he had to make sure that he can answer at any point questions regarding people having deposited money with him. This is the reason e.g. Mtgox has the requirement for ID verification before one can do substantial transactions in fiat.

According to the laws, if there is any money laundering going on (which Simon cant know as he doesnt have any dependable information on users identities) he makes himself an accomplice to the money laundering as he did not take sufficient measures to try to prevent it.
Converting fiat from phished accounts to bitcoin is money laundering, so some certainly happened.

Even an unwitting accomplice to money laundering, who frivolously failed to notice the money laundering (e.g. insufficient precautions) , can be sentenced to up to two years of prison time (!).

So in contrast to what Simon said a bit ago, he is certainly responsible, for operating a platform that could easily be used for money laundering.

Three days after the polish account was blocked (!) bitcoin24.com went down. During the big trading hype Simon already knew that his main business account is blocked.

Probably after the site went down another investigation was started, this time for fraud, accusing him of trying to run off with his customers money. This accusation seems to be at least partly based on his potentially careless and regular use of the Commerzbank account to withdraw cash, and also at least partly probably on his closing the platform and hence denying the users any access to their BTC and fiat.
Some news media report that he supposedly tried to withdraw a large amount from his Commerzbank account. That could be either:
- trying to run off with it or
- knowing that the account will be frozen soon (the polish one already was), trying to get some of his customers fiat to safety
Maybe the attempted big withdraw didnt happen at all, didnt find a good source.

The search warrant basically also states that they accuse him of, since sometime in March, not being willing and able to pay back all his customers deposits anymore.

The second accusation could be just a fuck-up of the way he dealt with the trading engine problem, though from reading his posts he might have been a bit careless in doing regular cash withdraws from the Commerzbank accounts (which doesnt really help to dissuade authorities from thinking about money laundering and/or fraud).

The first one is rather serious, as many people have noticed already, as he certainly did not operate bitcoin24 according to european regulations, and might thus be an unwitting accomplice to money laundering, which is still a very serious offense.