The Hidden Blade Assassin's Creed in Depth

(Second vid below the fold)

Pre-exposed blitz
About 2.8 seconds from the white flash to the first frame of the kill animation.
Using techniques first discovered by AKHeon (and more recently by Aurel), it's possible to get outside the invisible walls at Majd's execution stage. Once you cross the wall, what I call 'ghost mode' is initiated. Altaïr can do very little in this mode, aside from moving, the only thing is using in low-profile.
I put Altaïr in an elevated position right next to the invisible barrier and then drop down. The trick is to grab something on the other side of the barrier. Altaïr will then pull himself through, effectively breaching the wall. (Doing this with memory walls gets you desynchronized, by the way.)
Now we're in ghost mode. I'll get an article detailing that (along with a video) up soon. The special thing about ghost mode is that NPC's won't notice Altaïr at all, except for one. This NPC is Malik, so I go over to the bureau. You can use to climb onto certain structures. The wooden thing I use in the video is one of them. After that, the way to the bureau is clear. I show that you can use high-profile actions in the bureau and go to talk to Malik.
Afterwards, NPC's notice Altaïr again. You can make out some of the sentences in the video ("How about you turn around and go away?" and the like). This is also the reason why I pre-assassinated all the archers in the area, to minimize risk (setup time is like 10 minutes real-time, if everything goes well). In any case, I use the route shown in the video to get back into the execution area to start the scene. There are a couple of tricky parts.
2:57 Altaïr can't just walk up that small step, so I drop down and get up to momentarily unlock high-profile actions (it's like when you are running and then release , Altaïr takes time to slow down to a walk), to get up.
3:24 This is pretty difficult at first. You have to make sure Altaïr's hands are positioned just right (both as much to the right as possible) and then push the directional stick to the northeast.
4:00 You have to make sure to grab the ledge correctly here, point the directional stick to the northeast, not just to the east. If you fail to grab the ledge, you have to go all the way back to the place you climbed up to the roofs originally. This is also why I took out the guard post, to make my way back while guards could see Altaïr should things go wrong.

The guard normally standing in front of the door is gone, although you can hear him speak at 4:20. He reappears for the scene. Since guards react to Altaïr now, all that is left is to piss off part of the guard post in front of Majd. They will leave their place and start attacking Altaïr. I use the crowd to block them, since Altaïr still takes damage like usual. There are a few tricky parts in there, but it's just moving around a bit and seeing if you can find a place.
Once the scene ends, Majd will immediately draw his sword and jump of the platform. Since the guards have already vacated their posts, it's possible to sprint directly onto the platform. A stylish air-to-assassinate brings Majd a swift death.

All in all, the complete technique is pretty difficult to pull off. Out a lot of tries (and I mean A LOT), I got it right exactly twice.

Ghost mode
When I first discovered how to get out of the area, I didn't immediately go on to perform the blitz, since I didn't know it was possible. Instead, I wandered around the city and tried as much things as I could think of. That's how I discovered that you could scale those buildings and that talking to Malik would make Altaïr able to be exposed. In the video I show off some of the more fun qualities of ghost mode. Altaïr is able to stand next to a Templar, as if they were best friends, walk through guard posts, walk into jar-carriers and take a stroll with a patrol.
Fun stuff, but not very useful.