I think this is what takes time -- they have to build more than a circumstantial case that the crime was committed and as you said the suspect is not going to confess so they have a large hill to climb.

Flying to an island on his plane (even after everything we know about that has happened on that island residence) does not itself indicate any wrong doing -- they have to fond more evidence that links the threads together. If they charge or show their hands before they have enough it sets various clocks in motion that can harm the long term cases.

I have faith they are still working as many of these as they can looking for charges -- its only faith.