You open the door and there is an underground door that will lead you to the tunnel.
you have to apply for the job, then when you make it he will give you the key to the supply room
When it is night time and you have gotten into the supply room from the tunnel you need the key to unlock the door.
with the supply room key
To get into the Supply Room You have to get the Key from The Person who hires you
you don't use the supply key to the cottage!! you use it to the supply room when you get the job! later on you will get that key (to the cottage) and the key will say that it goes to an unknown place or smtng
In the supply room
nothing
You have to fix the 4 paintings and the assistant curator will give you a key
the security guard in the security room gives it to you
you have to get a job at the muesam to get it.
You need to apply for a job at the museum, get accepted, work at the forensics lab, and receive the supply room key.
there is a key, you have to click "use" and it will open.
Once you are applying for the museum job, don't wander off before taking the Forgery Detection training. When you finish the training, you are hired and get the key to the Supply Room.
Don't run off to the Supply Room right away. You only get the key after you complete the "Forgery Detection Training". (see related question)