I am somewhat surprised, but not completely, by the delay in an arrest of some sort.
We actually know little of what happened. Although widely reported that the stepbrother is a suspect/POI in this case, LE has never made such a statement to the best of my knowledge. The source of this information was Anna's stepmother in a filing in a child custody case. Obviously, she or her lawyer felt this information would help her case in some way. She said that she was told her son might be arrested. We do not know the context. Did LE volunteer this information, or was it the response to a question she asked? For example: "Are you going to arrest my son?" "We are looking at all possibilities and if he is at fault we will arrest him" is a very different scenario.
The information we have about security cameras came from Anna's grandmother who was not on the ship. This is at best second- or third-hand information. She also told us he had "demons" in the past, but never further elucidated. Does he have issues that would mitigate a crime, or make him incompetent to be prosecuted?
The weird Facetime encounter related by the ex-boyfriend is troublesome, but really needs follow-up questions.
Many of the witnesses are foreign nationals and may not be easily accessible to investigators, some may have returned to their home countries (very few American citizens work on non-Hawai'i cruise ships).
One tidbit I would really like to know is how different family members reacted on the Sea Day before their return to Miami. Were they all sequestered in their cabins? Was anyone in the containment area? Were they doing the limbo by the pool?
On thing that surprises me is that they all seem to still be on the same page. If I was in her father's situation, I would have kicked my wife and all her descendants out of the house and installed a high-tech security system; or taken my descendants and moved well away from her. Either they don't care, have secrets they don't want revealed, or more likely, they know something that changes the narrative.