Let me put it this way:
1. Who killed the people? (the killer, and no one else)
- what contributed to their decision to kill?
- what enabled their decision to kill?
2. If the <agency> had:
- decided and done <X>, would the outcome have been different?
- had <Y> resourses, would the outcome have been different?
- had <Z> training, would the outcome have been different?
3. Could other Agencies have contributed?
- if so, what communications systems would enable the contribution?
- if there are privacy issues, how do we overcome them?
- do the other Agencies need inter-agency exercises to facilitate cooperation?
4. Are there ways to identify and de-radicalise these shooters?
Moving away from blame, towards understanding Responsibility and Contributing circumstances prevent people from blaming and thinking no further
- they're at fault, I don't have to think further about this
- it's their fault, I don't have to problem solve
- they're to blame (so don't have to look at integrated solutions)
....towards looking at the factors that contributed, and dealing with the problem in a holistic matter. After all, if you have the same contributing factors, you will eventually get the same or similar outcomes from other people (not just with the person you blamed)