From The New Yorker:
As the C.I.A.’s assessment was making its way through the government, late this summer, current and former military officers and consultants told me, a new element suddenly emerged: intelligence from Israeli spies operating inside Iran claimed that Iran has developed and tested a trigger device for a nuclear bomb. The provenance and significance of the human intelligence, or HUMINT, are controversial.
“The problem is that no one can verify it,” the former senior intelligence official told me. “We don’t know who the Israeli source is.
The briefing says the Iranians are testing trigger mechanisms”—simulating a zero-yield nuclear explosion without any weapons-grade materials—“but there are no diagrams, no significant facts. Where is the test site? How often have they done it? How big is the warhead—a breadbox or a refrigerator? They don’t have that.”
And yet, he said, the report was being used by White House hawks within the Administration to “prove the White House’s theory that the Iranians are on track. And tests leave no radioactive track, which is why we can’t find it.” Still, he said, “The agency is standing its ground.”