The FBI opening a case does not guarantee that someone will be charged with a crime per se, but the timing of this announcement coming weeks after the collapse, not hours or days after, suggests its not simply a procedural matter. Rather that something was found and given to the FBI to investigate further.
0: https://www.ntsb.gov/investigations/process/Pages/default.as...
> a probe that will look at least in part at whether the crew left the port knowing the vessel had serious systems problems, according to two U.S. officials familiar with the matter.
https://www.washingtonpost.com/dc-md-va/2024/04/15/balitmore...
Often things like this are a technicality somewhere, where the FBI needs the funds unlocked to do X Y and Zed and the way to unlock them in this case is a criminal investigation.