That’s the fun part, you can’t. A lot depends on the details here. You’re looking for a one-size-fits-all answer to a very not-one-size situation.

In 99% of cases a major crime like a kidnapping that I know I didn’t have anything to do with should be reported immediately, and “speaking to the police” only ceases when I become aware they have decided to suspect my involvement. In the other 1% of cases, I have understood how bad it looks and I’m talking immediately to the best lawyer I can find and letting them do all the talking from the beginning.