A Mediterranean couple sought in connection with Williams' death is now considered a "red herring" after further police inquiries.
Organisers of the ladies fashion course Williams' enrolled on in secret will give statements to the inquest too.
The lawyer for MI6 says calling corporate witnesses will "paint a picture and set the scene".
Two experts have tried to reconstruct how Mr Williams could have got into the bag and locked it - The coroner says he wants a live demonstration in court.
The issue of whether or not Mr Williams could have got into the bag and padlocked it from the inside "goes to heart" of inquest the coroner says.
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Industrial vacuum cleaners and magnetic wands will be used each night during the summer to remove metal particles, dust, oil and grease.
Detective Superintendent Fiona McCormack said the Hotpoint FF175BP model had not been subject to any product recall.
Security for this year's event on July 8 has been reviewed following a spate of terror attacks in the capital.