So where is the 3rd aircraft?
At a guess I would say its probably in a hangar somewhere while the owner is being interviewed by the AAIB. I took an interest in this because I thought it may have been someone i knew. However this doesn't appear to be the case so my thoughts are with the friends and family of those who were involved.
Re TCAS: I saw a system built into the Garmin 1000 which is fantastic but it will only work when everybody is Mode S equipped. Its very similar to a TCAS but doesn't give "Resolutions" only "Cautions" and a display of local traffic.