Originality is something to be prized in any form of writing, and certainly in crime fiction. The snag is that it is very, very difficult to be truly original. Even when you firmly believe you've come up with something absolutely fresh and new, all too often it turns out that you've been beaten to it, generally in a work that you weren't even aware of.
This sense that I needed to come up with something absolutely original held me back when, in my teens (yes, I started early) I thought about writing a detective novel. I didn't know how to create something that wasn't likely to be derivative. Inhibitions of this kind are not helpful, and I only got over them properly when I came up with the idea of writing a number of mysteries about a Liverpool lawyer. Something I knew for sure had never been done. Even then, one reviewer of my debut, All the Lonely People, thought she detected the influence of Raymond Chandler (which I wasn't conscious of, I must say, and I'm not sure she had read much Chandler or indeed much crime fiction).
I also imagined that I'd come up with a great idea for my first book that combined plot development with snappy social comment. A body would be discovered in a municipal waste heap, picked over by impoverished scavengers. Very good - except that, many years later, someone told me that G.D.H. and Margaret Cole also wrote a story about a body in a waste heap....Similarly, one of my early short stories about Harry Devlin included a plot device that I discovered, only very recently, to have been used by Gladys Mitchell.
These things can make you despair, believe me - but there's no sense in despairing. The stories by Cole and Mitchell are little known, but that's not really the point, either. The real issue is that I was trying to do something very different in those two Devlin stories than they were trying to do in their books. There have always been similarities between story ideas that appear in different books. There are said to be Russian and Swedish books that anticipate The Murder of Roger Ackroyd, and one American mystery anticipated And Then There Were None. These were not, I'm sure, conscious borrowings, but rather ideas that were somehow in the air and which were developed by writers in different countries. Similarly, one of Dorothy L. Sayers' best plot ideas also occurred to Ronald Knox while she was working on her book. Another resembled an idea used (in a similar setting but in a different style of story) by Freeman Wills Crofts.
The same thing applies when there are overlaps between contemporary books. For instance, there was a vogue a few years back, after a drought in England, for crime novels in which bodies were discovered when the waters receded (very different from England 2014 - perhaps we are in for a spate of 'flood' stories...) I remember one Northern writer being rather cross that Reginald Hill had written a book about 'mystery plays' not long after she had done the same. But it was a mistake to be cross, in my opinion. The books were quite distinct, and I could give many other examples of overlaps which seem to me to be not in the least problematic. The real challenge for a writer is to come up with some element - be it voice, or character, or an aspect of setting - that is fresh. Trying to come up with at totally new storyline is wonderful when it happens - but it is rather uncommon, to say the least.