The mission log says I have the key to the foot locker (but it is not in my inventory) and when I click on Silas's foot locker I can't open it. See the screenshots below.

I was also really confused by this. This is either a bug or entirely misleading. I had to look this up in my play through to find out where to get the key (it's sort of in an obvious place). I can't remember if the key is obtainable until this step of the quest, but I'm thinking not.