How do I get the grey uniform out of the lock

Hint 1 of 5:

There's a key on the second floor.

Hint 2 of 5:

It's past one of the guards on that floor (at least when I played).

Hint 3 of 5:

It's inside a chest.

Hint 4 of 5:

Inside another, smaller uniform.

Hint 5 of 5:

Look inside that uniform, and you'll get the key.