Grizz; I am expecting some more info today. From what I heard both a/c were on Bamako frequency, the 737 never reported a collision and later used " security" reasons to avoid landing at Cotonou and divert to Malabo"
the HS 125 never replied to ATC calls after crossing the 737 and it was Bamako that alerted Dakar of the radio failure ( not uncommon in this area) The collison occured in non-radar coverage so which aircraft was at the wrong assigned altitude is unknown. (the 737 FDR migt tell us this if it has been secured )
As to the HS125, where did you read/heard Dakar followed them on their transponder ? if yes then they must have been able to follow its altitude , which one, if it was constant, slow or abrupt descent, etc.. did not hear anything about that.
Like you I do not buy the "fuel exhaustion." at 50 or even 100 NM off the coast pas destination. must be more to that.
A malfunctioning or set on OFF or SBY transponder would explain the non-TCAS event. But then again the 737 FDR could tell us if an TCAS TA or RA was issued, if we ever going to see it..