This achievement can be missed.
Once you have gained access to the butchers, you will see the pigs heads set up in front of you. Holmes will task you to find some blades to make cuts with. When you return, you will control Holmes and be tasked to make an incision with each knife to see if it matches the murder weapon. You are only required to make one cut per knife. With the first knife, make as many cuts as it will let you - approximately nine. The game will then automatically put that knife down, and unlock the achievement for you.