Question - from reading the posts here, it appears the helicopter has two separate fuel tanks? If so, I'm assuming that if the fuel was contaminated, the two engines would be less likely to be affected at the same exact time, which would effectively rule fuel contamination out as a cause. Correct?
Second - this is a real long shot, but. . . If the craft was flying at a low level, is there any way they could have woken/startled a flock of birds which were nesting for the night, with the birds then taking off in mass and being ingested? Could that have caused a sudden double engine failure?