Dave Lutz of Stifel, Nicolaus recounts what happened just before 6 AM, when things started to follow apart:
...Futures were having a nice morning till around 5:45AM, when almost $1.4B printed in DAX and ESTOXX futures – knocking the DAX off almost 2%, and taking US futures down 50bp. No headlines associated, but no recovery when Germany’s Factory Orders printed better (despite bearish chatter). We “Hear” that a heavy buyer of DAX futures between 7800 and 7850 on Monday got stopped out at 7800, and lighter single stock volumes could not support the weight. There was nothing in Credit or FX to correspond to the move.
Meanwhile, it was a rough night in Asia, as the Hong Kong got slammed on Bird Flu fears, and war rhetoric hurt the South Korean market.