Mean Streets, stuck

I’m unable to find

Any key to unlock the cabinet. I’ve looked under everything, especially in the green/NE house twice.

The walkthrough says

The contents of the cabinet are critical later.

Any help? Thanks!

Are you sure you have examined everything in the green door mansion?

There’s a particular item that you might miss psychologically, because it doesn’t get its own sentence describing it in the room description, but rather is mentioned in the sentences of other objects.

EXAMINE DESK.

Ooh! Thanks.

Ironic that I even tried umbrella ALL commands like SEARCH and L UNDER, but I didn’t try X ALL, because of course that’s not useful.