I came across this gem of a book cover …
A Gem of a Murder published by Dell (1959). The book was also published in hardcover by Heinemann as The Diamond Studded Typewriter.
“There is nothing so bizarre about The Diamond-studded Typewriter. It’s a straightforward fairly mild New York thriller about the search for a smuggled necklace, which several interested parties believe to be hidden in an apartment where the smuggler was killed. The only novel thing about it is the hero’s profession. He is no ordinary private eye but an Examiner of Questioned Documents. Let us hope that in future books he will be allowed to make fuller use of his professional talents. Questioned documents are more interesting than questionable diamonds.”
Sounds to me like the reviewer had a large cache of diamonds secreted up his rear passage.