I would have anticipated that a strike like this would be followed by a demand for the release of the current hunger-striking PA prisoners -- either accompanied by the dead bodies of the teens or not. The previous kidnapping by Hamas (and by Hezbollah) were kidnappings of military personnel. The distinction is fairly important. Israel does not swap for civilian hostages, but they do engage in prisoner exchanges.
Based on extremely limited data, my speculation boils down to:
1. The incident has nothing to do with Palestinians. It was a random act by some psycho.
2. It was a lone-wolf or splinter group that for some reason have not claimed credit.
2a. It was some external group that has not previously operated in Israel, like ISIS, that is trying to score a major coup by taking the war to "the Zionist entity."
3. It was a planned operation by Hamas or allied group that was disrupted by the massive search and response or by realization that one of the victims is an American citizen.
4. It is an act by an Israeli provocateur to trigger a backlash against Palestinians, similar to the incident with the grave desecration some years back.
But the longer this goes without any clear indicator of Hamas involvement, the less likely it seems. Again, unless there is some kind of intel that the Israelis have that they haven't made public.