... it's not like there is much room for it to fall any further. And by publicly demanding answers from Israel, the European countries involved ensure that there is no damage to their reputation and security. And of course Israel was at least involved in this bungled action. If there a good chance of being able to plausibly deny involvement, the Israeli government would do that. And if they really weren't involved, why on Earth wouldn't they? Saying "I (personally) did not know" and "There is nothing to connect Israel with this" is not the same as saying things like "No employee of the state of Israel took part in this assassination as". In the language of diplomacy, such non-denial denials are as close as you get to outright admission of culpability.
Obama says world must reach climate deal in Paris 'while we still can' (Reuters)
from the article: Germany, France also request Israeli answers on Dubai fake passports