How does math relate to the investigation in general and to Lord Peter Wimsey's investigation in particular?no
Investigation methods for both public and private investigators often includes mathematics. Perhaps the most important mathematical skill for an investigator would be computer programming, specifically for recovering lost documents or emails. Investigators of fraud other financial crimes are often accountants, who must have detailed knowledge of business practices and transaction methods. Mathcan be important in all kinds of investigative work, but it is more important for those in the financial sphere.
In The Nine Tailors Lord Peter Wimsey solves the "mysterious cipher (page 173) by trying various cryptographic methods, such as "skipping letters in accordance with a set combination of figures", (p 175), skipping every other letter, assigning a number to each letter and adding the results, etc. Wimsey knows that the cipher is related to the bells in Fenchurch St. Paul, so he goes up to the belfry to get the information engraved upon them. Wimsey also uses a bit of set theory in figuring out which person had which set of keys to get into the belfry and into the churchyard. Set theory works with groups of numbers, which can be related to people-- in this case the various people who had the various sets of keys to Fenchurch.
Significantly, in The Nine Tailors Wimsey discovers that the number of letters in the cipher formed a multiple of eight, and he related it to the pattern of bell-ringing. With this information he and the Rector solved the cipher.