This is for a criminal case. The victims don't play a prosecutorial role here and are not actually parties to this case. The appropriate venue for the victims

This is for a criminal case. The victims don't play a prosecutorial role here and are not actually parties to this case. The appropriate venue for the victims is a civil jury trial (lawsuit), where recovery of losses is possible because the victims then become party to the case (plaintiff). The reason this lawyer is requesting this is so that the government will be forced to lay its cards on the table during trial, which provide much stronger proof/evidence of Boeing's wrongdoing (which otherwise would likely be much harder to discover), and make it far more likely for a jury to award a huge award to the plaintiffs. So this is completely rational on the part of the lawyer, but the judge doesn't have to go along with it at all, and might not.