Google can't file criminal charges, only federal prosecutors can.

What would cause them to initiate it? What initiated it in the Jawbone case?

Generally the entity that believes their stuff has been stolen goes to the authorities to complain. Then someone there makes a determination whether or not to take up the case and ultimately prosecute.

Not sure if this is the same case, but Fitbit’s 10-K from a couple years back mentions an ongoing suit against them and some employees for the same thing.

https://www.sec.gov/Archives/edgar/data/1447599/000144759916...

CTRL+F on that page for “On May 27, 2015, Jawbone filed a lawsuit”

In the Waymo v Uber case, the judge referred the case to the Dept of Justice. The DOJ then decides if they're interested in investigating. They still might.