The key to this puzzle is one the of the six suspects in the game Cluedo (Clue in the USA).

Their surname only is used. As in all Playfair Ciphers, any repetitions in the key are deleted.

EB HS SL GU CB EU UA HX LH FU IP AH

CX DC RW OQ VU XN CR IP ZX BW

OR RA BL MU IP BM ST RY EU SL XE SR

In decoding remember:

Go up, not down. Go left, not right. Start on the same row for diagonals.

As in all codebreaking, look for repetitions. 

The following page may be helpful:

Common digraphs