Old symbian phone + this = /thread
Surely you'd get a really crappy, if any, picture from a camera in the letter box?
Put explosives in your letterbox, the thief is the one who is splattered across the far wall the following day.
Easy, just blame the letterbox.There is a slight problem with that, namely extreme bending of the Explosives Act and committing murder.
Aside from that .....
You could buy some permanent dye and post yourself some in a waterproof jiffy bag - once opened the thief will be literally RED HANDED, then catch him at the weekend.
Alternatively you could post yourself some kind of beacon device and keep the transmitter, maybe like a remote rape alarm or car key finder? Then go round all the rooms and listen through the doors while transmitting.
Easy, just blame the letterbox.