That't the way it has to be. When people working in an agency or department are accused of committing a crime, particularly against co-workers, the leaders of that agency/department can't be allowed to investigate it themselves. I know human resources is there, and major organizations have legal teams which COULD handle the cases if they wanted to, but the leaders won't want to admit that they let such crimes occur on their watch, and open themselves up to lawsuits. So independent legal agencies and people have to take these cases if they're going to be investigated and solved honestly.