Sacrifice of David

My first post, just got to say, loving all the varied discussion here. I have seen an image of David in a different ampule room, carrying a round container, than the one with the majority of the crew, which is where i'm guessing they make first contact with an extra-terrestrial lifeform. What i'm wondering is, do they perhaps take some kind of item from that first chamber, resulting in casualties, which they then entrust to David to return to the SJs. My theory would be based on the fact that, as far as I can tell from the trailers, it looks like David is the only one to actually enter the SJs ship, as in the star-map and teloscope/gun room, where he says " They're leaving..(to go where) Earth". This would also correspond with the images of someone disembarking what seems to be the Prometheus and being blown violently through the sand-storm carrying a similar looking container. This also makes me wonder if David is actually the catalyst of what hinders the SJs, as they don't expect this synthetic being to so brazenly board their ship, transporting a lifeform that even they aren't familiar with?? Or am I just getting too excited thinking about this film....