Apart from the 'cesium' being the wrong color (silver-grey instead of light brown), there should also be much more of it. Cesium has an extremely low density of 1.93 g/cm³ - a little over two thirds that of aluminium. The volume of half a pound of it would therefore be at least 129.5 cm³, or 4.5 ounces. A lot more if it was coarse grains.
The German policeman has the wrong crest on his uniform - in Berlin, it would show a bear, not the red cross.
The material Shaw and Cole think is Cesium could not possibly be used to build a "dirty bomb". (Nor is it Cesium, which is so reactive it has to be kept in oil.)
Cesium is a highly reactive metal and will explode on contact with water, meaning it could theoretically be part of a bomb, but it is not radioactive which is a necessary trait for use in a "dirty bomb".
Caesium-137 is a highly radioactive fission product and could be used to create a dirty bomb in large enough quantities.
Caesium-137 is a highly radioactive fission product and could be used to create a dirty bomb in large enough quantities.