If you shoot a bunch of people while declaring allegiance to an organized group known for shooting bunches of people then I think that pretty clearly demonstrates that reading your communications has a pretty high likelihood of turning up something useful in preventing future incidents. If this doesn't clear your hurdle for reasonable search then what would?
To be clear, I don't think the order to Apple is necessarily altogether a good idea or is even going to produce the desired results, but your complaint seems to be with the fact that this data is being pursued at all.
Edit to reply:
> Evidence of a conspiracy would help. You said they declared allegiance to an organized group. When they did that, did they say or hint that they had been in contact with that group, other than, say, watching public YouTube videos?
The woman in the couple declared it right before the shooting[0]. Do you want a notarized letter from the deceased?
> Would you agree that "high likelihood" is too low a bar for justifying searching the phones of people who live in high-crime neighborhoods?
I'm pretty sure neither "high likelihood" nor "authentic need" were being used as a term of art here, but I would bet that any judge would view the commission of murder declaredly for an organized militant group to be probable cause that there is information pertaining to more criminal activity by that group on these two's phones and in their communications.
Do you really view this as a government overreach or are you just trolling? Under what circumstances, if any, would you see as justified a search of someone's email? phone? house? So far you've equivocated between living in a bad neighborhood and committing murder-suicide.
[0] http://www.nytimes.com/2015/12/05/us/tashfeen-malik-islamic-...