brian606,

Assuming most young adults carry at least a cheap cell phone these days, was there any record of an urgent emergency 911 call from any of the occupants?  So far, and it's now been quite awhile, there's not emerged a peep from HPD confirming this.  It follows then that a high speed run to the hospital or fleeing from an assailant can be almost eliminated from consideration.  That leaves a catastrophic mechanical or electrical failure of some kind.  I will grant that a determination of such remains pending, however, we all need to keep in mind that while Occam's razor can be overused, sometimes it does lead us to the truth, however unsettling or unhappy it may be.