readynas pro business lost files

Hi there and indeed, thanks in advance!

RAID 10, 4 drives. Raidiator 4.2

i decided to split a folder into two on the drive by creating a new folder and copying half the original over to it.

i left the computer and when i returned, done.

at this point i should add it was not my computer and i cannot guarantee whether or not anyone had sat down and did anything to it while i was away for a few hours, though i'd imagine not.

There are now some files missing. i have removed the drives from the NAS and into two double cradles and tried various recovery softwares (on a read only basis!) to look for these files but to no avail. could they have been in use by someone at the time of copying and thats the root cause of the problem? Obviously i have now backed up the data after the fact! lesson learnt. anyways......any ideas on how to find them? i cannot imagine them having been written over. 

Thanks for any help and advise

andy