Evidence in one case can be used in another. It's interesting that they filed this now, before they're coming close to the two year statute of limitations. Because they can't force him to answer questions or reveal evidence that could incriminate him criminally.
But perhaps they don't think they need to. They can use this to question witnesses and perhaps get info that could help them in the custody case. And also as some have suggested to try to freeze assets.
And to possibly assist in some ways in the criminal case.
It's interesting. They know a lot. There's a strategic reason for this.
It's going to be an interesting case.
ETA! Sorry for using the word "interesting" three time!! As you can I'm highly curious about what's happening in this case.