Parents couldn’t find a babysitter so they sedated her to go out to dinner. She suffocated sleeping face down or choked on aspirated vomit. They disarticulated her, stuffed her in a suitcase, got rid of the body parts and made up the kidnaping story as a cover.
On a similar topic, I don’t know if the Lindy ‘a dingo took my baby’ Chamberlain case has been brought up ITT but Australian friends have suggested that the child was murdered by a jealous sibling, the parents disposed of the body far from the campsite, and blamed it on a dingo. The absence of blood trails, paw prints or drag marks that would have made tracking the animal extremely easy with a flashlight, even in the dark, seems to be a lingering question that Chamberlain’s defenders don’t like to talk about.