David did not create the Xeno

@Deep Space

Once again.. indeed i think that has to be close to the Ball Park.

@Myrddin365

Very good solid points

@Goddamn Tropics in here

Indeed the Original was Bio-Mechanical.. even though the Egg and Face Huger Stage was not....  Maybe a Lindeloff could come in and have Kane actually be a Synthetic Construct working for the company lol... Joke ;)

They could lead us anywhere with this, its a Big Mess for sure lots of inconsistencies...  I think the movie teases David or Walter role.... But i think its maybe a Red Herring..

Who knows... the Xeno was around before... due to LV-223 and the Mural... but these could be related DNA that has not yet got the Mechanical/Synthetic Part of the Bio-Mechanical Look.

So they could show the Derelict was a ONE OFF... a Event where something infected the Space Jockey.. similar to the Chest Buster Cryo-Sleep Engineers in Prometheus.

His Ship Crash Lands... and the Black Goo Cargo gets compromised and Split and leaks all over and something somehow .... in this ONE OFF Accident Creates something that causes the Bio-Mechanics.... Over Time the Ship degrades and is infected... where its once Mechanics are now Fussed with the Black Goo and something that trigger this to happen or Evolve over time...

But we dont know for sure where they are going....

The Egg Silo is a inconsistency... unless as stated before we have Tardis Type Technology at play.. (God forbid Time Travel part too).

Maybe it could be described as landing on a Cave of Sorts and well the Mechanics get infected with the Black Goo so that now the Synthetic Elements are merged with the Black Goo and we get basically Bio-Mechanical Transformers kind of stuff going on... where the goo now operates as Nano-Parasite/Synthetic and can build Machinery too.

Or maybe something like this EXISTS... and the Engineers Re-Engineered off it...

As far as David...

He could re-create something similar.... if has the knowledge and tools..

And maybe the Bio-Mechanics are just a ONE OFF Event?

But Ridely had teased we would find out why it was Bio-Mechanical and a Weapon.... which seems to indicate the Xenomorph was purposely created from something to have those Bio-Mechanical Features...

I think loosely we can get clues... but i am not sure Ridley would give on his Promise.. well Comment we would find out exactly Why/Who created it and HOW.. i think some Mystery will be kept... at least until he ties it up with the Last Movie

my take on a WMD is total destruction, not replacing one creature with another. unless ofcourse u have no intention to ever set foot on that world again in which case it doesn't really matter. but my take on it all is the engineers create man, man becomes aggressive and r seen as a future threat so they decide to wipe us out but the goo is meant to possibly be dumped in our water, maximum impact as we all need it to survive but life would continue and evolve again. xeno's mean a hostile world that would be uninhabitable by anyone again so doesn't tie in with the perception given of the engineers at the beginning of Prometheus. the xeno also is a total fluke of circumstance and the mutation of fiefield and the worm also as they are infected in a different manner. OR...... this is what is meant to happen and the original goo has been altered and we were to be test subjects?????

Its pretty open really.....

Indeed the possibility is  the Engineers created Mankind without Permission of their Hierarchy, or the Engineers decided to interfere and evolve us or teach us stuff and get us to worship them against the will of the Hierarchy.

Maybe Punishment was sent to those Engineers.. this failed... the surviving Engineers then re-weaponized it to use against their creators... and then proceed to try and get Mankind to worship them.. 

We we proved as rebellious and loyal to them as they was to their creators..... or Hierarchy..

They realised the Punishment that lead to the Ancestor to the Xenomorph... lead to something they then saw as a more Perfect Creation than the intended Creations... and that the Mural Deacon/Xeno was either seen as the Perfect Form from Engineer Sacrifice...  or this was the aim.

So they then saw the Mural Organism DNA as being more Perfect than their own Engineer DNA.... and decided to use this to Evolve Life on Earth....   being as though we had evolved to a point that displeased them.

@BigDave very plausible. It's fun to have all these ideas about the back story, but frustrating when none of them are confirmed or denied in the film.