Audit log
An audit log is an append-only record of who did what in a system and when.
For a case file the log matters most when something goes wrong: a document is missing, an export went to the wrong recipient, a deletion is disputed.
The property that makes a log worth having is that it cannot be edited by the people it records. A log a user can rewrite answers no question at all.
Related: Chain of custody, Provenance
Legalnaut builds this out of your own case file. See the plans.