I read Gemma Dowler's heart wrenching book about her sister. Yes - Bellfield was initially arrested for unrelated charges after his brave partner accused him of rape. The police had been on the verge of having to release him after the 96 hour limit, despite knowing he presented a danger, because they didn't have enough at that point to charge him with Amelie Delagrange's murder.
It took even longer to convict Bellfield of Milly Dowlers murder. I believe a lot of the evidence there was circumstantial. Placing him living at the place she went missing and his partner recalling he was out that night.
There were no forensics at all as she wasn't found for 6 months. All her family had were remains. Less CCTV back then as well.
I have a lot of hope in the fact Libby's body was at least found much earlier and should at least give some information. If only in eliminating some possibilities. There is lots of CCTV. There must be other stuff as well. And there is the luxury of time.
Let's just hope.