The GAO report was obtained by the Institute for Research: Middle East Policy, a group critical of pro-Israel advocacy in the U.S. See “Nuclear Diversion in the U.S.? 13 Years of Contradiction and Confusion,” U.S. General Accounting Office report EMD-79-8, December 18, 1978.
Update: The most recent account of the case is “Revisiting the NUMEC Affair” (sub. req’d) by former NRC officials Victor Gilinsky and Roger J. Mattson, Bulletin of the Atomic Scientists, March/April 2010.
“The circumstantial evidence supports the conclusion that the HEU ended up in Israel,” said former NRC Commissioner Gilinsky. “Our conclusion, which was based on a lot more information and analysis than was available to the GAO in 1978, thus goes well beyond that of the just released report. Moreover when we talk about the HEU we include not only the unexplained losses found in the famous 1965 inventory, but also unexplained losses for the subsequent few years, which are even larger.”
“The bottom line of the article,” said Dr. Mattson, “is that it is time to end FBI and CIA secrecy on the now 40+ year old Apollo/NUMEC affair.”
https://fas.org/publication/gao_numec/
On September 10, 1968 NUMEC receives a key coordinator of Israel's clandestine nuclear weapons program
(Avraham Hermoni) and three undercover Israeli intelligence operatives. NUMEC tells the Atomic Energy
Commission the Israeli visitors are "energy specialists."