Sounds like the airline lost cabin pressure. The same fate the befell Payne Stewart. The windows were frozen over. Hopefully they had all "fallen asleep" prior to the crash and didnt feel any pain or panic.
When an airliner loses cabin pressure, the temperature drops rapidly and there is lack of oxygen...called hypoxia. It is possible, from the comment above where the cousin text messaged a relative saying it is very cold and the pilots are unconscious, that it sounds like that is what happened.
http://www.airsafe.com/stewart.htm
Payne Stewart Accident Information
Both pilots and all four passengers, including professional golfer and 1999 U.S. Open winner Payne Stewart, were killed in the crash of a Lear 35 jet near Mina, SD on 25 October 1999. The jet, originally on a flight from Orlando to Dallas, strayed off course over northern Florida and continued flying to the northwest until the fuel apparently ran out.
U.S. Air Force pilots reported that the cockpit windows were obscured by frost. The conditions of the windows are consistent with a loss of pressurization and a subsequent rapid drop of temperature. It is likely that the pilots and occupants may have lost consciousness due to hypoxia, or a lack of oxygen. Between the last communication between the aircraft and air traffic control and the aircraft's final descent, the aircraft was reportedly flying as high as 45,000 feet.