Originally Posted by Mouse
Thanks guys. You know, I reckon I could write a few thousand words from the killer's PoV without revealing they were the murderer yet anyway. So. Write it and see, I suppose!
If it's not a key part of the book that the murderer's identity is kept secret, to the extent that it's revealed well before the end, you still need to take care when building up to the reveal. The reader may not want to feel that they're being teased or lied** to, particularly if this isn't the general way the book is written.
** - If the murderer has the sort of mind that thinks murder is just something that they do without thinking much about it, having one or two longish scenes where it never crosses their mind might work; otherwise it will look like some sort of prank on your
part, and getting the reader to think about the author is probably not what you want.