Murder Rural England 1890's

The county police force. This Wikipedia entry gives a reasonable overview of the development of policing in the UK.
http://en.wikipedia.org/wiki/History_of_law_enforcement_in_the_United_Kingdom

Many county police forces have history societies that can answer more detailed questions
or read some Sherlock Holmes stories

What Waylander said. If you are using a specific location check that the County boundaries have not changed.

Also, check out the Jonny Depp movie Sleep Hollow. He played a variation on Ichabod Crane where instead of a school teacher he was a law enforcement agent stationed in New York City in the year 1799. But then he had to travel all the way from New York City up to the tiny hamlet of Sleep Hollow to investigate a murder/decapitation.

There is an atmospheric element to that film that might be of assistance to your world-building.

You see ... [Plot Device attempting to defend the outlandish notion of viewing a horror film for assitance with crafting a non-horror story] ... the world-building that movie undertook included an element of fish-out-of-water. We start with Depp (Ichabod Crane) at home in his normal environment in New York City. And then we see him get dispatched by his superior to go and investigate a ghastly murder of unspeakable detail that happened in some little farming town up the Hudson River from them. So we see Depp leaving his normal environment (the "civlized" city) to go into this alien environment. That was an important world-building element of the film because we were being asked to relate to him and to the city world that he initally deemed "normal." That allowed us to more thoroughly relate to his ill-ease and general inability to fit in upon reaching the town of Sleepy Hollow.

This is a little off-topic, but if you're writing about 19th Century crime, then there is no better book to have on hand than William Roughead's CLASSIC CRIMES (here's a $7 copy on eBay). A Scottish lawyer, born in 1870, his book follows several crimes from murder all the way through the trial. The time periods range all over the place, but he's a great writer, they're very accessible descriptions and the details are the kind of thing you won't find anywhere else.

Here's the page about CLASSIC CRIMES from the New York Review of Books with lots of pull quotes and ordering info.

I think it's one of the greatest resources for someone writing about mayhem and murder in the 19th century.