If a bomb of any kind was involved, I imagine autopsies would show this to be the case. However, have autopsies been done?
According to this CBS news piece
Satellite detected heat flash at time Russian jetliner went down - CBS News,
A Russian government plane brought 130 bodies and partial remains to St. Petersburg. The city is holding three days of mourning through Tuesday.
If true, it seems the bodies have been removed from Egypt to Russia before detailed examination could be done? And how could those bodies have been definitively identified as Russian - given that four were from Ukraine and one from Belarus?
The article also suggests that the USA has not been invited to participate in the investigation:
White House press secretary Josh Earnest said the U.S. offered support for the investigation, but he added that he's not aware of any resources that have been dedicated to it so far.