Never mind murder confessions -- what happens if there's legally privileged information in a safe deposit box? Seizing documents without providing any opportunity to litigate privilege is a legal Pandora's box.
This happens all the time in searches, and, unsurprisingly, there's a bunch of very well-defined processes in the DOJ for handling privileged information found in searches. You should follow Ken White's podcast and Twitter feed if this is an interesting topic for you.
There's well defined procedures for searches which may run into privileged materials, yes. In the case of searching law offices, the first step is "don't do this if there's any way you can possibly avoid it". If a search is absolutely necessary, you either have documents reviewed by a "dirty team" who are walled off from the "clean team" who only see documents which are determined to be unprivileged... or you seal everything without looking at them until a judge hears applications to have documents returned.
It sounds like in the case of seizing these safe deposit boxes, no such procedures were implemented.
No, there are well-defined procedures for searches that turn out to uncover privileged materials, too. If you think about it, this issue must come up all the time, in all kinds of searches.
A Google search will rapidly avail here, including DOJ's own handbook for how to handle this situation. It comes up a lot!
The problem here is "turn out to". Documents in a safe deposit box might well be privileged but not in an obvious way because nobody expects their safe deposit boxes to be searched by the FBI. The FBI may have seized privileged documents without realizing it.
