No telling ...
Whoever did it was looking for attention, yet didn't intend to hurt anybody. (This time)
Reports I saw said a report of gun shots was called in to bring police so they could be the target of the explosion. I believe whoever set it intended to kill police and civilians alike and as many as possible. Hopefully, they will be caught and executed after getting every bit of possible information they have.
Why broadcast a warning if they wanted to hurt/kill people? The hoax gunshot call would have brought the cavalry if that was their goal.