the third officer
He had pencils in his luggage, and a pencil sharpener (knife). There was (what looked like) graphite powder on a brush found in his luggage, the same black powder is visible on his tools’ protective wrappings.
The Tamam Shud slip was thought to have been cut away from the Rubaiyat using scissors. A pair of scissors was found in his luggage.
The slip was found in his pocket.
A penciled code was found indented on the back of the Rubaiyat, the book was said to have been found near the scene. The indentations were made when the code was written on a piece of paper placed on the back cover of the Rubaiyat. A piece of paper cut to the same size as a page in the book. Cut with scissors.
He was thought to have been a ship’s 3rd officer.
Always write your messages on a piece of paper placed on a glass surface. SOP.
The bloke who wrote the code was an amateur.