This is a text guide with a relatively easy way to complete the Bangkok mission with Silent Assassin. I did this on Professional, but I supposed it can be replicated on Master as well to unlock the "classics" challenges for Master as well. When doing this on Professional, I ended up 6th in the global leaderboards.
You'd need the deadly poison vial and some coins. This means no fibre wire, but you don't actually need it.
- Start from default location.
- Enter the hotel, go left, and head to the plate of food that Morgan will always eat from. This should be the rightmost plate on the middle shelf.
- You've now taken care of Morgan since he'll eat from the plate later, and die. This would be considered an accident kill with no impact on SA rating.
- Head to the bar, which is just to the left of the starting location.
- Run all the way to the end, enter the door (trespassing), and toss a coin at the container.
- This lures a staff into the area. Subdue, dump him into the container, and take his disguise.
- Run back into the hotel, and take the stairs that's to the left of the food that you poisoned earlier.
- Head to the room when Abel is at, and hide in the side room via the balcony.
- Once Abel goes to the balcony, toss a coin the the side room to lure him, subdue, and take his disguise. You should drag him to the corner of the room near the door to avoid a "body found". Take note though if you take too long in the mission, his body will eventually be found still, so be quick.
- Exit the door, and run across to the other side of the hotel.
- When on Professional/ Master, there are cameras all over the stairs, Make sure you avoid them when going up. If on Master, you may want to use your one available save before you head up the stairs.
- Go up the stairs all the way until you reach the recording studio.
- The recording booth is right at the end. Head there, and grab the wrench that's found on some boxes. Wait there.
- Cross will go into the booth soon. Sneak in, and throw the wrench to his head to subdue him. Snap his neck when he's down. If you simply run in to subdue and snap, the noise generated will lure someone into the booth to find the body.
- You're done! Retrace the steps (avoid the cameras) to the hotel entrance, and leave by the boat.
Hope this helps. Have fun!