HCW has only said that there is no video, picture of the act with both MM and CB on camera together.
The act, I presume, means the murder.
There still may be pics or a video of MM on her own, that do not show/identify CB in them.
If so, this would be classed as circumstantial evidence, from which Judges could infer what happened to MM, after putting together the number of circumstances that BKA has, to create a chain of circumstantial evidence.
If there was a pic or video of both CB and MM together that would be direct evidence (fact), just like the abuse pic he had of his GF's little girl in which he appeared.
JMO