What's particularly odd about the police essentially dismissing the Brentford canal sighting as a viable deposition site for SL, is that the location of Gallows Bridge is situated south of the lock where the GUC meets the river Brent.
In other words, the section of waterway in which the man claimed to have witnessed JC dumping a suitcase, forms part of the River Brent and not actually the Canal which connects with the river further north.
So, if the case was dumped in the River, then it may have acted differently in terms of currents and depth.
Did the police do a thorough enough job to search for SL in the river Brent?
The river feeds into the Thames further south.
What's also interesting, is that Gallows bridge is easily accessed via the A4 road, which joins the Fulham Palace Road further east.
So it may be possible that after JC took SL to a lock up/empty flat etc..., he then killed her and shoved her into a suitcase, and then drove her north up Fulham Palace road, turned left onto the A4, but instead of joining the M4 motorway, he stayed on the A4, and then took the side road, parked up, and then quickly accessed the river Brent close to the Gallows bridge, by walking along the grand union canal walkway.
He could then run back up to the side road, and then turn directly back onto the A4.
Just a theory of course