Not a test device, per sé. Rather, a possible test run of the main charge. The explosive material in the Central Park bomb was determined to be TATP, a ridiculously powerful, notoriously sensitive peroxide-based explosive (most peroxide based explosives pack quite a kick). It was sensitive enough that the act of stepping directly on the charge provided enough heat, shock, and friction to cause the high order detonation. No detonators were found because none were needed.
I haven't heard anything official yet about what the main charges were in any of the specimens recovered. However, at the Elizabeth station, someone said they smelled gunpowder when the one pipe bomb went off during the robot interrogation. It could be that he only had enough TATP for one or two devices, or he could have stayed away from TATP altogether in favor of a less sensitive main charge. There's a number of possibilities when you don't know what the evidence has indicated so far.
I have to give a lot of credit to my LEO EOD brothers and sisters. Lots of solid work involved, with no loss of life (except maybe the robot). From the RSPs, to site and evidence exploitation, everyone came together so that the LEO's could bag this asshole. They've earned their beer tonight!
