SPOIL :
- The weapon is at the beginning to your left, behind all the containers.
- The key to the fence is on the roofs, you have to climb the blue barrels and then the air conditionner.
Yes, the game was supposed to take place at night, but I added too much assets for my computer. When I clicked "Bake Light", Unity told me "35 hours left" ... so I disabled all the lights and now it takes place during day ^^'
Thank you for playing and commenting!