It would appear that this stock has been heavily and very successfully shorted. They are in a strong position due to the weakness of the company (GMAC is a mess with lots of toxic crap, as noted in a wsj article yesterday) and the strength of the shorts' position is obvious (note the churning high volume). They are like roaches and will be hard to exterminate.
Their hold has been very successful today. They are fighting over real wealth here. When they finish they will probably own tens of millions of very cheap shares imho. These are defense industries in disguise and will not be allowed to fail. The democrats won folks. lol