Since I made a lot of screencaps along the process of completing the mission, I might as well throw stuff together here.
First, unless you have already done this: Watch the briefing.
Next, click on this image below the video:
It will lead you to holding.macheist.com/evidence where you'll find a pile of stuff.
First, click this yellow bar:
It'll give you the an envelope, click it again and a piece of paper will appear. Click again to enlarge it, it contains hints (like #7: 8 S on a S S, which means "8 Sides on a Stop Sign") on putting items in the correct spots. You can figure this out on your own, or use this image:
http://files.seems.nl/images/evidence-2 … 015022.png
NOTE: If you can't see the whole thing your resolution is too small, which happens to be the case on even recent MacBooks, so chances are you need to zoom out using cmd - or View > Zoom out in the menubar.
After you've put an item in it's correct box, a small piece of paper will appear over it, you can click them, but you don't have to. When you're done with all the items you'll be taken to a new black page with all the pieces of paper. If you put these together it'll read "portalplayer". Put this in the time machine bar at the top:
Note: If you're not seeing this bar, try clearing your cache and start over.
Voila, done. You'll be taken to your loot and you'll find the debriefing in your briefings page.