One of the most difficult things for a thriller writer to do is to plan ahead to hide evidence in the early stages of the story development. Then, like leaving bread crumbs behind for the gumshoe to discover, you have to be careful where and how you spread them. I often find myself giving away the ending at the half way point in my novel. Then thirty thousand words later I realize what I have done and spend hours and days trying to back track re-hiding the clues. The investigation had been over and all the characters knew it, except for me. There are two main types of clues that trip me up. The first is the verbal clue where a sub or secondary character says something significant to the plot. The second is the placement of physical clues...and then forget where you put them, or that you even added them.
I tend to do a lot of sub plotting , braiding story lines through out the novel, and then bring it all together at the end. So far , I haven't left my private investigator scratching his head, wondering how he solved the mystery. Do others have this same problem with clues?