Thinking about your situation Mouse, kind of illustrates a dilemma I've always had with my writing.
On one hand I would like to eke out surprises and secrets, as others above have said lay a trail of breadcrumbs, and come to a 'stunning' crescendo in a reveal.
But it really takes a lot of skill to be subtle! And to my experience what is a trail of breadcrumbs to me, is a inconsquential dusty floor to others. To take this analogy to breaking point, I feel when writing that I actually need to lay a trail of hot bacon sarnies all wrapped in fifty pound notes to get the readers attention
So I'm thinking a bold reveal early on helps to simplfy the narrative (in a good way) and takes most of your readers with you, whereas a more complex gradual reveal may be more difficult and tricky and may run the risk of alienating readers more.
Also although I don't know your narrative, revealing the identity of the killer seems to me to be a great way of transitioning from the 'Beginning' to the 'Middle' of the book - automatically the plot dynamics and reader expectations have altered in a stroke