It is somewhat akin to the flocking mechanisms of bird flocks (or crab swarms, whatever).
A good strategy might even be to follow the swarm in terms of coming predictions:) .
To my mind there are two main reasons - some insider's manipulation which reasons we can never know and the global markets recession which makes people to cash out and wait for some better times in the economy.
The manipulators are not coming from the insiders but in fact it has been coming from the mtgox itself. mtgox trustee becomes the real reaons who is manipulating the bitcoin market at this time.