When Fermin escaped from the prison - what was the point of him stealing his cellmate's "treasured" key when he didn't know what this key opens or where to use it? Also, when the cellmate found him 20 years later and Fermin just meekly handed the key over (why would he?!), how/why was the locker empty with all the "riches" gone? Where did that money go and why was this not explained?!
Daniel He gave the key back to his cellmate because he threatened to tell the truth about him not being dead, why he took it in the first place I wouldn't know. But the fourth and final book of the series is yet to come, so lets hope we can find some answers there.