Library books are arranged by the Dewey Decimal classification scheme whereby each subject is represented by a number.
You wil find books on the same subject will have the same number. The shelfmark is preceded by the letter D and will be followed by 3 letters, which are usually the first 3 letters of the author's name.
Here are some useful forensic science shelfmarks.
D 362.293 & D 615.1 & D 615.788 Drugs of abuse
D 364.12 Criminal investigation (detection - documentary evidence, fingerprints, hair, blood…)
D 364.128 Methods of criminal investigation
D 364.3 Criminal psychology
D 364.128 & D 614.19 DNA analysis
D 615.9 Toxicology