The door won't open.

Hint 1 of 5:

You need a device to help you out.

Hint 2 of 5:

Did you check all the display cases and cabinets yet?

Hint 3 of 5:

One of them has a dagger in it.

Hint 4 of 5:

It's the one to the left of the telephone booth.

Hint 5 of 5:

And you have a key to open it.