The way I took the statement that he was retiring was simply that this case (and the others) are going to be held up in court for the next few years, and they have time for a new prosecutor to come in and learn the case(s) without it jeopardizing anything, where if he were to wait for arrests, that could pose problems. Basically, I feel like he is tired, has seen too much, maybe these cases are just too much. He has seen the evidence and crime scene photos and suspects etc. It's the worst of the worst when it involves children. So sad, but in many cases with babies or teens, it is career ending for some of LE and even prosecutors.
I thought it said, or maybe someone else had said it here, that he didn't expect any arrests this year, but the reality is, that's a little better than what? 6 weeks and its 2018. Courts slow down over Christmas and the holidays. Even if they do make an arrest before the end of the year, it's going to move at a snails pace. Better to get out now, let someone else get in and have this "slow season" to become intimate with the cases. Fresh eyes may be exactly what this case needs. I commend this prosecutor for not being driven by the need to go out on a "high note".
JMO