“We were not convinced initially, this would be treason for an Arab security apparatus to be involved in this," Hamas Lebanon head Osama Hamdan said of a report in the Al-Hayat daily.
The Arabic daily said an Arab country had given the Israeli spy agency Mossad information about the movements and habits of Hamas leaders abroad.
"Now, because of what happened yesterday or through other information, there are indications that this may be case," he said.”
I would bet on Jordan, or perhaps even the Syrians themselves. Who else would have that kind of information? And why would they share it with Israel -- what would they get in return? Hell, you can't even dismiss the possibility that it could be Egypt considering the difficulty it is having in negotiating with Hamas these days, and the fact that it will sooner or later have to confront it in Gaza if the pullout takes place. If we're lucky, we'll known in ten years. If we're not, we'll either never know at all or find out soon enough after someone gets assassinated.
Update: It looks like they think it's Jordan. And some people do think they will hit back:
Hamas may retaliate by striking outside Israel, ex-ambassador says:
Retaliation against Israelis outside their country could follow last weekend's assassination in Damascus of a Hamas official, a respected Canadian analyst on the Middle East said yesterday.
"There will be a tendency to explore overseas operations," said Michael Bell, former Canadian ambassador to Israel, the Palestinian territories, Jordan and Egypt”