T246951: CU 2.0: Eventlogging for Special:Investigate [8Hours] asks a number of questions that involve needing to know when an investigation has finished, including: How many users are under investigation by the time the investigation ends?.

As described in T246951#6145812, adding a "Done" button was discussed as a solution (albeit an imperfect one).

Some questions to consider:

• Where should the button go? (It should be on every page, so with the button group on the top right?)
• Where should the accompanying text go?
• What should the accompanying text say?
• What should happen when the button is clicked? Should it force an end to the investigation?