I've read so many times, iranians couldn't make A-bomb because of a fatwa. Why B.Ms didn't got that fatwa? I think effort to acquire the N-bomb has been there for a while but iran is under a severe watch and would have been attacked anytime they were really closer to acquire one, just like now.
Pakistan lied through thier teeths when we were developing one, so are the iranians under the same compulsion. Developing the weapon works as a deterrent, it doesn't mean iran had to use it, khomeini fatwa remains, but iran is constantly developing the technology required and even trying to make the weapon itself. But the enemy is watching very closely, and it's just not that easy.