We’d all like to think we know Suzy, however, her work colleagues didn’t and maybe even her brother RL only had a small insight into her private life.
There are police detectives that can read criminals, and IMO Detective MB is one of those.
He was the only detective (to may knowledge) that realised that Shorrolds was a complete mistake. He made this assumption early on, but I can only assume wasn’t listened too by his superiors.
Again IMO he read JC like a book, and picked up on the mistakes he made in the interview.
Okay JC was inept, but sometimes even evil criminals have luck on their side. I don’t think JC was anymore careful with Suzy’s deposition than SC or SB, the only difference being he was lucky.
Look at the Melanie Hall case, the perpetrator just dumped her at the side of the motorway. A few metres further in and her remains would never have been found.
Maybe JC did just that, or given his love of water no one found her in the Brent river
section of the canal.