There is considerable mystery surrounding this crash. Allegedly, the first people on the scene were all dressed in white protective overalls who prevented access to anyone else. There is some speculation that the aircraft may well have been carrying either beryllium initiators for nuclear devices, or weapons grade plutonium when it crashed. This would explain the necessity to remove the material immediately, and might also explain the outbreak of cancers and lukaemias which are alleged to be a result of this.
Though some element of radioactive hazard has never been ruled out, there are others who attribute this to depleted uranium U238 in the aileron mass balances which was a common practice when this aircraft was built.
What has never been satisfactorily explained is why a cargo only aircraft could so easily have ditched in the Isjelmeer probably resulting in zero deaths.
I think that the crew were extremely concerned about the nature of their cargo, and its fate should the aircraft be lost.