That almost tells me it's not Jihadists. Calling in the threat would cause an evacuation. Jihadists are about body count on top of the destruction, so there would be no warning.
They also don't leave the packages. They strap the packages to their chest and/or belt and detonate them.
I don't know who it could be, eco-terrorists, neo-nazis, prank, could be anything or nothing, but it doesn't fit Jihadist m.o.
The Provos always ring in advance.
Not necessarily. The Madrid bombers just left backpacks on the trains. There were no suicide bombers, although most of them were killed later when they blew up the house they were staying in so that the police couldn’t take them alive.
Agreed. Unless they’re trying to bring about a particular political result, but even then, as in Spain, it usually takes a body count to make a nation change course, and they understand that.