I am not buying that its Prater. The Ripper was active during Praters childhood. It would be challenging for Prater to be a serial killer as is, as we have seen time and time again being a serial killer is physically demanding, even for Dexter who has been caught off guard and overpowered several times. No way Prater, as a child, was doing it. However, it could be that theres someone else, maybe someone we havent met yet, who is close with Prater, thats the Ripper. Maybe Prater is an accomplice and The Ripper is, similar to Trinity, a bit of a misnomer because its two people doing the killings and not a single killer.