From news reports since the 1940s we know that there have been no reports of nuclear warheads going off without the sanction of their owner governments so far.
However, the laws of probability tell us that this may not be the case in this century or the next.
Therefore since the laws of probability are not on the side of the citizens of earth this century or next, it behooves all governments on earth to redouble their efforts to prevent a non-Government sanctioned nuclear blast.
For, if it ever happens it won't just be a building in Baghdad or Kabul or Islamabad going up to a suicide Terrorist, it will be a whole city. And if that ever happens will the genie be out of the bottle and will we peaceful citizens of earth ever be able to put it back? So redoubling the efforts of world governments right now to prevent the "accidental" nuking of a large city might be the single most important thing any nation can do.
When it comes to nuclear weapons, precedent is everything.