The explosives were put in pressure cookers before they were put in the trashcans.
Now for my fellow military folks...YPOC (yellow palm oil container) and pressure cooker IED's are used primarily where?
That was noted as soon as they made disclosure pressure cookers were used.
You look at the delay in blasts, and the affects of that (people running toward the location where the second blast occured). The packing of the duffle bag with nails, etc. for maximum damage.
This is not two college students pissed off at the government.
I don't think this is a wait for their reaction type of sample run either. I think this is how they can attack, and how they will attack going forward.