France’s government had earlier asked prosecutors to investigate Israel’s alleged violent mistreatment of activists from the Gaza-bound Global Sumud Flotilla, potentially opening a route for criminal proceedings.
Something happened, the article source from France24 is missing (it was there when I posted).
changed the source to reuters
Because France has no jurisdiction over Palestinians
There are dual citizens on both sides in that conflict (even though in majority on Israel side). So there is an obligation to investigate as par IHL.
Edit: On a side note, each country which had a boat submitted to piracy in international waters is entitled to respond to it as an act of war.