SCOTLAND YARD: A HISTORY OF THE LONDON POLICE FORCE'S MOST INFAMOUS MURDER CASES, by Simon Read, is an entertaining history of the London police agency, covering a lot of ground with very clear historical exposition. It begins with the Ratcliffe Highway Murders in 1811, before London had a police force at all, and began to push the government toward creating such an agency, which was founded in 1829.
Each chapter then describes a case or two and the ensuing investigation, some successful and some not. It turns out I've already read entire books about a bunch of these cases, in books such as THE ITALIAN BOY by Sarah Wise and THE SUSPICIONS OF MR WHICHER by Kate Summerscale. Luckily I read those books over a decade ago so revisiting the investigations here wasn't a problem.
Crimes rose and fell in frequency over time. The 19th century had a lot of murders committed as part of a theft or con job, though the Ripper murders were a startling break. Trains gave more mobility to criminals, who could attack a passenger or escape by train to a different city. Boy, there sure were a lot of trunk murders in the 1920s and 1930s!
In the late 19th and 20th centuries the Metropolitan Police began adopted new scientific techniques: fingerprinting, chemical analysis to identify bloodstains and poisons, forensic medicine, and ballistic analysis.
Overall I thought this was an enjoyable historical-crime book that was factual while staying pretty light.