How does one get a pressure-cooker to explode? What was the explosive?
I assume the terrorist didn’t have a long electrical cord for it, with a pot-roast cooking on the sidewalk....
Gunpowder (black powder) or smokeless powder. Electrically fired, so there’s a battery and a short circuit/hot wire in there somewhere.
From the amount and color of the smoke, and the orange flash, I'd wager strongly that the explosive was old-fashioned black powder, the nitrate, sulfur, charcoal mixture you can buy in up to 50 lb kegs from any good reloading store.
You don't need a blasting cap to detonate the stuff, a spark will do, and it has a faster burn rate than normal smokeless pistol and rifle powders. It deteriorates fairly quickly, (Short self life), and it's highly hygroscopic.
I'm guessing a simple electrical timer wired to nichrome wire as an initiator.
It more than likely had a cell phone or timer on it.
I tried a little research on the subject and found that the Pressure is used to confine the explosion until pressure builds up , making the eplosion much more powerful.
It has little to do with the pressure cooker itself exploding and more to do with the mechanics of building up pressure.