Here’s MrFreeze2244’s walkthrough for not just completing but also attaining Silent Assassin in all levels of The Somsak Equation
, which is currently the only escalation available in Bangkok. All credit for this video goes to the marvelous MrFreeze2244.
My approach differed from the video. I found it easier to always start undercover in the kitchen as a Kitchen Assistant. This option unlocks at Bangkok mastery level 9, so I highly recommend unlocking that starting location before doing this escalation.
I relied only on coins, and for kills I always grabbed the cleaver which is right behind you when you spawn. It's very satisfying both as thrown and as melee. Freeze uses the lethal syringe on the head chef, and in later levels where you have to move all bodies into the freezer, he uses the fiber wire, because his approach is always to kill the chef where he's standing in the middle of the kitchen.
You may do this, or you may be more comfortable using a coin to lure him into the small office that's in between the kitchen and the utility room. At one point a different kitchen assistant goes into that small office to check inventory, so be careful. I always subdued him which freed up the option to lure the head chef into that office.
Also keep in mind that target Phet Rardchawat's patrol always brings him into that utility room, so he will come to you. Be careful with your timing of moving the bodies into the freezer so he doesn't catch you in the act.