And that slap was so satisfying.
Someone kidnaps your child after lying to you, claiming it's not yours but theirs, and falsifying "paternity test", and then abusing it?
...and all you would be happy with is slapping them?
This is why we have justified use of lethal force laws in our "modern" country. Depends when you found out, and sequence of events, but it's permitted to use lethal force to stop a felony in progress (such as kidnapping).
Keep that in mind when it comes to the police interview.