Leon - the superfluous letters you get from the clues spell the names of four individuals who are responsible for the 'disappearance' of the four unclued entries.
'CZO-' seems as if it is rubbish, but it's not! It's the start of a surname...
The fourth name should end ...WALD not WAD. (the 'L' comes from the Rods of Head Master clue). Make sure you start your numbering from the top left hand corner of the grid as per a normal crossword.
I hope I haven't given too much away...keep thinking about people who might be responsible for the 'disappearance' of other people and you'll get there....