By looking into the database leaked from Mt. Gox you will notice two obviously special users, one is "TIBANNE_LIMITED_HK", and the other is "THK". Both sold about 2.96 million bitcoins during the time period from August 2011 to the end of November 2013. They never bought any coins. Additionally they didn't pay any fees.
What were those special users for, and where did they get their bitcoins from?
One might think the Tibanne users were established to sell bitcoins earned from transaction fees by Mt. Gox. But that couldn't be true. According the the leaked database Mt. Gox collected around 180,000 bitcoins from fees during April 2011 to November 2013. Besides that this is an average of 0.34% per trade. Since the leaked database contains no information from before April 2011 we estimate the fees collected in the early days by summarizing the trading volume from historical data found here and applying an average fee of 0.5%. That leads to additional 18272 bitcoins. So the total earned fees by Mt. Gox were below 200,000 bitcoins.
The question remains: Where are the 2.9 million bitcoins from?
By principle there is no need to have 2.9 million bitcoins to gain a trading volume of 2.9 million bitcoins. Let's say Tibanne did business on Silk Road, sold drugs for bitcoins, sold the bitcoins on Mt. Gox, someone bought the bitcoins on Mt. Gox, bought drugs on Silk Road from Tibanne, and so on. Just by circulation a few thousand bitcoins can bring in a trading volume of some millions.
However, one thing's for sure. The Tibanne users took a big part from daily trading volume on Mt. Gox. Their trades made up in average 6.29% of total volume. On some days they peaked over 30% as seen in the following charts.
Considering the fiat withdrawal issues on Mt. Gox since June 2013 there was high demand to buy bitcoins in order to move money out. May be the Tibanne users prevented the price at that time from rising much higher.
And still, the question is open: Where are the bitcoins from? Did Tibanne Ldt. simply operate a mining pool? Were bitcoins bought on other exchanges? Or were bitcoins (GoxCoins) just created out of thin air? Nobody but Mark Karpelis knows what was going on .
If you want to take a closer look on the Tibanne users you can download here a tab separated .CVS file with summarized information of their activities on a daily basis.
The claim that the Tibanne users never bought any bitcoins is probably false. As statet here there might be a bug in the Mt. Gox logging software that lets those Tibanne useres appear only sell bitcoins.