Prosecutors can visit crime scenes for multiple reasons, but it’s almost always a while after the crime has been committed and not when it’s fresh (as is the case here).
The prosecutor’s presence COULD mean charges are forthcoming, but not necessarily. The prosecutor most often visits a crime scene in preparation for eventual charges and a trial in order to get an up close and personal feeling and memory of the crime scene itself (as opposed to just relying on photos). Also, sometimes when investigators find something useful or perhaps incriminating at a crime scene, the prosecutor will visit to help determine just how useful or convincing that piece of evidence would be to convict someone. Maybe it’s the width of a door, or the scratch marks down a wall, or something of that nature that points towards the size of a possible suspect or just the proof of their presence at the scene. Kind of “we found this… can you use it and will it hold up in court?” kind of thing.
It may or may not be the development we’re all hoping for, but it’s definitely not a bad thing.