The main U.S. concern is that Russia is the source. Moscow has responded to fears that terrorists could use stray nuclear material to build a “dirty bomb” by promising to tighten security around its nuclear submarines and nuclear-research centers. The United States has long encouraged such steps. But last week the White House threatened to block a $40 billion appropriations bill if extra allocations–some designed to enhance security in Russia–were added, choosing instead to focus the package on domestic economic stimulus.

Even if extra funds are eventually allocated to help the Russians, it may be a case of too little, too late. Two Turkish men–Aydin Duran, 32, and Mehmet Aydin, 47–were arrested last Tuesday near Istanbul in possession of 1,150 grams of uranium, which they were allegedly trying to sell. Turkish police say the enriched uranium could have been used to build a bomb or, packed in a conventional weapon, to spread radiation. And it’s known that the two men traveled frequently to Eastern Europe and Ukraine, where they probably obtained the uranium. (They have already admitted to buying the uranium from a Russian supplier.) The good news is that Duran and Aydin don’t appear to have terrorist connections. They’re more likely a couple of entrepreneurs out to make a buck, say police. The bad news: others like them may well have already connected with Al Qaeda. In other words, bin Laden could be telling the truth.