[SPOILER] What you think about red?

[Thaliur]

Oh wait, your right. And we are just assuming that the zombie guy is grey. For all we know Grey could have made it deeper into the shelter.

Well, actually, for all we know, Grey could have died on the Chief chemist's examination table where he was tied down and killed using an excessive overdose of Insulin (three times the "certain death" dose was necessary, if I remember correctly).
I'm pretty sure Derren Grey is the Tuurngait we see from the dejà vu vent.