firstly you need to move his box and make sure he knows where the new place is, you can put him in it and leave it with the used litter in it, but scoop out the wet and poo. a hall is a high traffic area so he's probably trying to cover all the other smells there. he needs to have a litter tray in a private low traffic area. Secondly you will need to clean the area more than just with bicarb. you have a couple of choices. you can buy a product called Nature's Miracle here: Nature's Miracle Stain and Odour Remover Gallon

and use according to instruction which is to cover area with non diluted solution and let dry completely, no need for carpet cleaning machine.

OR

you can try washing the area with a bio washing powder then with a carpet cleaning machine and then covering the washed area with a white spirit like Gin or Vodka and let it dry.

you may also find he needs a bigger tray or it needs to be cleaned regularly. depending on the cat some are fussy.