After many frustrating hours of trying to solve something that couldn't be solved, I had to read an online walkthrough to know what I kept doing wrong.
When you go up to the landing platform, the walkthrough says you have to *kill* the 2 guards. If instead you *sneak up to them and run like hell when they spot you* like I did, you will just be in time before the red laserbarrier switches on. So I assumed this was the right thing to do, because the game continues after this point (with the Great Crypt photograph) But...you will never be able to transport back up to the platform, because the red laserbarrier will close immediately when you step out of the transporter and you're a sitting duck to the two guards (whom you should have killed before).
Is this a known bug? Why did they make it possible to sneak past the 2 guards? Did they not test this; I mean, you have to sneak past guards *a lot* in this game, so the game developers and testers should have expected people to try this.
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