Were they evicted? Why else would their stuff be still inside? Can't think of any other reason.
I certainly don't know the legal aspect of this, see reply 1, but I would have thought, if it took you 3 weeks to clear their things then that was ample time for them to contact you to collect their belongings. Did you leave them for the bin men? Take them to the dump? They have no proof really that you did anything with them, after all the house could have been emptied before you took possession.
Personally I think they've got a bloody cheek expecting you to have held onto it. I would also have expected a house ot be empty when I moved into it.
What state was it in when your viewed it?