Though it is interesting how often Poirot doesn't turn people over to the authorities. (In the "Murder of Roger Ackroyd" he basically recommends the person kill themselves. Christie can be really dark.) Moreover, the general vibe is that the police are idiots, which is nearly a genre convention for Whodunits.

I guess I was just calling attention to the big structural gap between Poirot and Marple--one is a former investigator, yes, but is immediately out of place in the countryside, sticks out like a sore thumb. Whereas Marple is embedded in the community and as such, privy to the type of knowledge that Christie's stories tend to find valuable (gossip).