The chemist from the last batch is under arrest and this crew, and these detonators are what was left over from the first bunch.
Since the explosives were already all used up, they improvised in a somewhat amatuer fashion, using the detonators that they already had and perhaps wrapped in nails and such.
Explosives are not chem 101, and you don't get any chances to muck up.
Magdy ElNashar was released and not charged.
Semper Fi