Illuminating matters of a peculiar nature
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I did not have time to analyse every artefact in detail. Below are some observations I made as I was packing your materials.
I have separated my findings for each artefact into 'First impressions' and 'Further information'. I suggest you read the first impressions first and look back at the documents to see if this helps.
If you need more advice from me, please go on to 'Further information'. I cannot guarantee my findings were correct.
Thank you for accepting case 371. The documents from this case were discovered in our vault. We are not sure how we acquired them. The Archive has a limited number of researchers and is aware you are an astute individual, so we decided to entrust this case to you.
The writing made no sense to me but I noticed some creases in the paper. Maybe it needed folding in the correct way to understand it. 
After a little folding this made more sense. The bottom section seemed like a riddle telling of locations to visit. I would like to draw your attention to the letter from Hector to Mary about the different creatures. This may mention the locations.
You maybe able to deciphered the symbols on the ribbon from the information given by Hector on his postcard from Athens. Laid flat and deciphered it made no sense.
I noticed on the post card Hector mentioned it was a 'Skytale cypher'. This is an old style cypher used by Greeks and Romans. When a ribbon is received it is wrapped around a stick of a certain size. Then the lines are read across. The first line to read starts at the arrow. Make sure you wrap it very tight. There is a link to more information about this type of cypher Here
I hope this was helpful.
Good luck with the case.
Raven Rejtély