Obviously it goes without saying that our thoughts here go out to those involved and I for one hope the cause can be found and action taken to prevent such a tragic loss of young lives in the future.
Much speculation has been made (here, in the Media and elsewhere) as to why (if?) the TCAS system directed the Boeing pilot to descend when the Tupolev was already in descent.
From doing a google seach it seems that there have been a number of occasions where a TCAS system has incorrectly directed a pilot to make a manouver that has put two aircraft on a direct collision course. It is only through the skill and judgement of the pilots (And perhaps good visibility) that a disaster has been averted.
It should also be remembered that last nights tragedy occurred during darkness..maybe if visibility had been better disaster could have been narrowly avoided.
Without wishing to pre-judge any investigation, serious attention needs to be paid to the TCAS system on board the aircraft and pilots need to be made aware that these systems are far from infallible.
More on previous TCAS "incidents" here:
http://www.aaib.dft.gov.uk/bulletin/jun01/cggwd.htm
http://www.rpi.edu/~woodhe/docs/wsj/flawed.txt
http://www.atsb.gov.au/aviation/rec/r19990159.cfm
http://news.airwise.com/stories/99/11/942324329.html