https://www.nytimes.com/2024/01/28/world/middleeast/gaza-unrwa-hamas-israel.html
Just note while you're reading this that UNRWA has 13,000 employees, so these 12 represent 0.09% of the total staff.
The Times has reviewed some of the evidence provided by Israel to the UN and US regarding the UNRWA staff that are alleged to have helped Hamas/IJ during the attack and following it. In at least one case they were involved in the kidnappings, at least one was involved directly in the killings at a kibbutz, and at least one handed out ammunition. 7 were teachers at UNRWA schools.
I should note that part of the ICJ ruling was an express order for Israel to shoulder a greater role in running aid distribution in Gaza given the insufficient aid coming into the region.
Interesting to contrast this response with our response to the Houthis in Yemen. Part of why they were removed from the foreign terrorist organization designation by Biden in 2021 was because of the threat of famine in Yemen and the effect of the designation on aid to Yemen.
It is also why recently the Administration did not impose it again, but instead chose only to impose the Specially Designated Global Terrorist designation.
Sometimes you have to make tradeoffs given the dire circumstances. I think this is a clear case where we should continue funding to UNRWA because there really isn't a good alternative.