This is a truely tragic event and my thoughts go out to the bereaved and the ATC on duty that night.
To correct a few inaccuracies that have appeared on this thread regarding STCA at LACC
1) T3C5 - The ALP servers (These provide the STCA warnings) are a dual redunant pair. If the PAS (Primary Address Space) fails then the SAS (Secondary Address Space ) will take over.
Although not considered a safety system the coding and testing of the application is the same as any other system. I was also surprised to find this out, but as someone explained you don't use STCA to control aircraft. Given recent events that thinking may change.
2) Ahh-40612 - STCA is unaffected during DD&C or NAS shutdown at LACC. The TDU has a complete set of Servers and these are running providing the same services as OPS (including STCA). STCA also works purely on Radar and therefore has no need for flight plan data.