Hi

If you are in possession of the  file containing the work sheet why not have
a look at the associated  macros in the vba editor this may some clues.

It may be that some of the macros exactly duplicate the code of the original
sheet. Check out variable names and range names  for parity between the
allegedly plagiarised material and the original script.. check out the
content of REM statements, those are likely to be highly personalised ...the
more parity  you find the  more of a case you can build. Perhaps the macros
still bear the name  of the original author as would be the case if  the
macro recorder had been used.

I cant suggest what you can do about it if do find  your colleague has
"stolen"  the code I think you would need to consult a lawyer about that .

Best N10