This version is later changed dramatically. The link for what has been revealed today will be provided, but it is so far just in Norwegian

Here is short translation:

It is not known if the tank was ordered to take position in the middle of the small lake or if their driving was more of a random choice. It is a known fact that they reversed six meters on to the 55 centimeters of ice and parked the tank. It is amazing that the ice can take 55 000 kilo if the vehicle is moving (the standard is 117 cm) but after a short time the lake swallowed the tank. The two Afghan veterans never made an escape because the tank slid under the ice and blocked the upper hatch. They had oxygen tanks and died not from drowning rather freezing to death.

http://www.dagbladet.no/nyheter/2006/03/24/461792.html