Odd... I figured out it was David simply due to the injuries on his face. Walter's regenerates (exception of his hand), so the guy needing to staple his face together made me already realize it was David with the fact that they didn't show the conclusion of their fight.
Sorry but the characters were too stupid for me to put this up with the Alien movies. Mr. Captain realizes that David created these hostile creatures and how David was talking to it just after it beheaded that lady yet he was still willing to stick his head into the egg sac.
Then Walter realizes what David had done much earlier, but gives not a single warning to those working beside him.
Also sorry, if you tried to take a ship down to danger levels with 2K people, I am going to knock your ass out and put you into hypersleep (or try anyways even if I have to wake some Colonists), the rest of the people on the planet can figure out what to do later.
I know they were probably focused too much about the Alien that was loose, but I would be wondering how the hell it got on the ship right after I killed it/sent it off into space. There was no way I was going to go into hyperspace without dealing with those concerns.
Issue with origin movies like this, is you already know how it will end. As soon as I figured out it was the origin of the Aliens, I knew the crew and colonists were screwed in the end as if David failed, it would contradict the Alien movies.
I knew it was David when they didn't show any killing blow. If there are identical looking characters in a horror-ish style movie and they fight and the result isn't shown on screen, it's always the bad guy. But yeah, the rest of the crew were dumb as nails. And what's up with that awkward shower sex scene at the end of the movie? Ridley has completely lost his touch.