It's groundhog day in Tehran. Another nuclear scientist, this one identified as Mostafa Ahmadi Roshan, who worked at the Natanz uranium enrichment facility, was killed when an explosive was attached to his car. Several questions arise:
1) Why aren't the Iranians attempting to kill Israeli defense officials? The answer, I believe, has more to do with Iranian technical limitations: Since the Iranian regime has no compunction about killing Israeli civilians (through its proxies Hezbollah and Hamas), I doubt it has reservations about attacking military or intelligence officials. Perhaps one thing holding back Iran, though, is fear that attacks on Israeli officials (or, even more consequentially, American officials -- though of course, Iran is already killing American soldiers in Afghanistan) would prompt an immediate Israeli strike on Natanz, before the regime is able to move its centrifuges to its underground facility at Fordow.
2) Does Israel, or whoever is assassinating Iranian scientists, believe that these killings will actually slow-down Iranian nuclear development? In other words, do the people behind the assassinations believe that Iranian nuclear knowledge is so concentrated in the minds of a few scientists that a limited series of assassinations can cripple the program? This doesn't seem likely, obviously.
3) Is the goal of the assassination program to convince Iranians nuclear scientists to seek other lines of work? This is also plausible, but not likely to work: I think the regime would take the Tony Soprano approach -- you can't resign from the Mafia -- and tell frightened scientists to get back to work, or suffer the consequences, or have their families suffer the consequences.
4) Why is Iran so incompetent at protecting its nuclear scientists? This is a perplexing issue.
5) Why is the Mossad, assuming this is the Mossad, so deft at assassinating people in Tehran? It's a very hard target, Iran, and the Mossad has on more than one occasion bungled assassinations in terrible ways (the attempted killing of the Hamas leader Khaled Meshaal in Jordan is only one case in point).
6) Another question, or something closer to an observation: If I were a member of the Iranian regime (and I'm not), I would take this assassination program to mean that the West is entirely uninterested in any form of negotiation (not that I, the regime official, has ever been much interested in dialogue with the West) and that I should double-down and cross the nuclear threshold as fast as humanly possible. Once I do that, I'm North Korea, or Pakistan: An untouchable country.