There is a fallacy in creative writing that in specific genres one has to outline. Thrillers and mysteries are both genres that staunch outliners will say that these styles of stories need to be outlined or else they won't be any good.
Case in point is Stephen King--even though he writes horror genre mostly, many of his stories delve into the mystery and thriller genres as well.
Okay, okay. Stephen King can do it, but he has to be it.
Beholder's Eye was written entirely without an outline. In fact, when I first wrote it, I didn't even know who the killer was--how odd is that! Halfway through the book, when I discovered who the killer really was, I did go back and tweak and foreshadow some of the earlier chapters, but hell that's what editing is for.
How about mystery writers? I read a book called They Wrote The Book: Thirteen Women Mystery Writers Tell All It's a fascinating read, and it's funny to note that some of these mystery writers are outliners--and are adamant that this is the only way to go--and others who discover the story as it unfolds.
Once again, I have to tell you that I do not outline but if you need to, go for it. Every writer is different, including you. Do what works well for you.