Whoever did it, I suspect they were surprised by the results.

Their design seemed to target high-profile folks or ones who otherwise would make lots of publicity (tabloid???). Almost like assassination attempts.

Yet the letters caused the most upheaval by passing through, or being found in, sensitive areas, and by causing innocent-bystander casualties.

I'm betting that if the perps try it again, they will tweak their approach based on what they learned.

And I'm sure that anyone on this prestigious board could design a more terrifying attack - even assuming only the materials used in that first attack - than the one that actually transpired. Of course, we have hind-sight working for us.