NTSB and FAA are at the site of Saturday's fatal accident. A TV interview with NTSB indicated that the only wreckage found thus far is the fuselage.

In addition, information from ATC (air traffic control) indicates that the aircraft had climbed to 27,000 feet before suddenly descending and disappearing from radar at about 7:20 PM local time (which is approximately 50 minutes after departure, putting it overhead the crash scene).

These two pieces of information lead to a couple of probabilities:
  1. A catastrophic failure may have occurred at altitude, causing the aircraft to break up in flight, or
  2. A malfunction or pilot incapacitation occurred, which allowed the aircraft to depart from controlled flight and exceed allowable flight speed and/or loads, resulting in an eventual break up.

Pilot incapacitation at altitude is often due to hypoxia, caused by a pressurization fault in the aircraft. This is an extremely dangerous situation as the onset of hypoxia is insidious and may not be noticed before crews become totally incapacitated.

In 2000 a Beechcraft King Air 200 crashed in Australia with the loss of 8 lives - probable cause; hypobaric hypoxia. After the pilot became hypoxic and unresponsive (evidenced by unintelligible radio transmissions, followed by silence), the aircraft flew on for another 4 1/2 hours on auto pilot before running out of fuel and crashing. See ATSB report:

http://ow.ly/fds3u 

In the case of the Cessa 421, it may have been flown by hand at the time of the in flight "mishap" that precipitated the crash chain of events - therefore the hypoxia scenario is plausible.

The evidence of missing aircraft components at the crash scene almost certainly indicate that parts broke away from the aircraft prior to impact. The challenge lies in determining the exact series of events that led to the point of break up.

Link to video story - CBS 47 TV:

http://ow.ly/fdpPk