aviadornovato, the reason 154 died is perfectly clear:
1) the two aircraft were assigned the same altitude, which is a normal and temporary occurrance when the two are hundreds of miles apart;
2) as they became closer, ATC should have reassigned one or the other to a clear altitude;
3) ATC could not contact one of the aircraft, and then failed to reassign the other.
The pros in this forum understand this sequence very well. There are a dozen other side issues (why the radio & transponder failures, etc.), but when ATC fails to act to assure clearance, the negligence is obvious.