I saw a documentary about this and I remember the key details were:
1. The bodies were radioactive
2. Official files with strict handling SOP’s were clearly tampered with
One theory is that they accidentally ran across a weapons research site and that the nature of the research was so sensitive that the research authority disposed of the whole group.
But that’s just one of several theories.
Hold the phone everyone——mystery solved: http://www.youtube.com/watch?v=9yeVivvo9KI
One further thought about the radiation. Since these students all worked in graduate studies at a polytechnic institute in the Urals, maybe they were all involved (or most) in secret government work with nuclear materials. Crappy safety measures would certainly been no surprise with Soviet SOP as far as I know. Radiation at what level? What kind of radiation? From what kind of materials? All unanswered and fitting with information suppression then and now.
Just my $0.02.
Yekatarinaberg is where the royal family were assassinated.