Highly-sophisticated bombs that killed 3 people?
The bombs were designed to injure and terrorize. They were highly effective. What was sophisticated about them was their ability to synchronize two separate and distinct pressure cooker devices.
The bombs were placed at street level, where they caused mainly severe leg injuries, including numerous amputations. Had they been placed higher, those would have become head injuries and decapitations... in other words scores of deaths.
It was the placement of the bombs that made them less deadly. The triggers and hardware worked reliably, and did show expertise. I'm pretty sure the investigation will turn up that a pro either trained them or handed them the triggers ready made.
I picked up on that one right away. A Freeper who claimed to be an electrical engineer posted a message on an earlier thread indicating that these bombs were not only very simple, but also exposed the two mutants to some potential danger because of the possibility of an accidental detonation when using a remote-control car detonation device like what has been described for these bombs.