One thing I'd like to point out here is that the societal definition of the boundary line between murder and justified homocide has changed a lot over the years. There were many circumstances historically of homocides occuring which were by no means carried out in secret which today would be considered murder but at the time may have been accepted by the community and considered justified.

Also you'd have to consider vigilante justice and lynchings as well. Consider that it was not uncommon for horse thieves in the old west to be pursued by posses of civilians who would then hang those they caught without a trial. Undoubtedly such rough justice occasionally swept up folks who were not guilty of the crimes they were hung for. Similarly, lynchings have been historically commonplace and very often resulted in the extra judicial execution of the innocent or of folks who were "guilty" of crimes that did not deserve death. Also, it was not uncommon for folks to take advantage of a lynch mob to further their personal greivances.

Such things deserve note when considering "murder" in a historical context.

In the 1800's, all you had to do was get as far away as you can as fast as you can. Police agencies were not connected like they are today. If you murder Suzie in Albany and ran to Syracuse before the law was on your tail, you'd be home free basically. The advent of the railroad system increased this flight risk. The police had strict jurisdictions and were often poorly trained, in part of public fear of a 'standing army', and the speed of the railways made escape much easier. Murder Suzie at 3pm in Albany and hop the 4pm train to Detroit and arrive hours later without the police non the wiser. Even if the Albany police had a clue that you murdered Suzie, they didn't have the power to bring you in on their own. They would need the cooperation of the Detroit police, who have no idea who you are, what you look like, and with no ID's like today, your basically home free again. The Pinkertons (during Alan Pinkertons time, before the bad rep of being strike breakers) were somewhat a 'national' police force. Because they were private, they had no municipal jurisdictions, providing agents the freedom to pursue criminals over county and state lines unlike municipal police. The Pinkertons had agencies across the country and were organized in a way that supported nationwide cooperation if needed. Alan Pinkerton actually foiled an assassination attempt on Lincoln during his inaugural train ride to DC, by receiving news from his Baltimore agency who uncovered the plot and by coordination his agents to ride the train and guard Lincoln, cutting telegraph lines along the railroad to stop any communication about the whereabouts of the train and having agents in the crowd searching for the suspects and then having the presidential train unexpectedly leave Baltimore in the middle of the night. The logistics of this operation were impossible by 1860's standards of police work, and were only used in the high profile case of thwarting an assassination of the POTUS. John Doe murderer would be long gone unless a family member of the deceased hired a Pinkerton.

You could read a good deal about this online in the book, "American Murder: Homicide in the early 20th Century."

http://books.google.com/books?id=63Et0WJR_ooC&printsec=frontcover&dq=American+Murder:+Homicide+in+the+early+20th+Century&hl=en&sa=X&ei=l1TnUpjlH4S-sQTl14CwBg&ved=0CCsQ6AEwAA#v=onepage&q=American%20Murder%3A%20Homicide%20in%20the%20early%2020th%20Century&f=false

Murders tended to be solved very quickly or not at all. Technology played a huge role in this. As you mentioned DNA evidence and fingerprinting weren't available. Also notably lacking were ballistics tests, tests for poisons, psychological profiles, and communications between law enforcement offices. If a murder was committed and the perpetrator fled, this would make a huge difference on the likelihood of his being apprehended- along with profiling, commonly used and shared mugshots, etc.

The text mentions that while murders between acquaintances was common, there was much less of the serial killing and sexually driven murders we see in modern times.