A brief overview of corroboration:
- 2 witnesses are required to corroborate.
- Technically a murderer making a confession, but there being absolutely no other evidence whatsoever, means that murderer could not be found guilty.
- CCTV / video footage / forensic evidence is not a 'witness'.
- expert validation of forensic evidence is a 'witness'.
- An independent third party reviewing CCTV and positively identifying an accused is a witness.
- Technically the same could apply to a helmetcam video. The person shooting it would be one witness (they saw it with their eyes) and someone (the police usually) identifying the suspect from the footage would be another witness.
- Helmetcam footage of a car passing too closely etc. is all fine and well, but if the driver is not positively visible and identifiable... How can there be a second witness? (unless you catch up and have a word through the driver's window, with there having been no chance for the driver to change).
Now, in something as serious as an actual assault I'd expect it to be taken seriously, and the 'positive id' from the footage to be useable as a 'witness'. Of course this shouldn't be necessary because the person suffering the assault, plus the filmer, are both witnesses. In this case the footage would be used as evidence in its purest form.
I do think the police are often easily bashed, and certainly there are some instances (that get publicised, and therefore make it appear the norm) where they could do better, but against the background of public sector cuts, low morale, and frankly the neddish muppets they have to deal with on a regular basis, I personally think they do a superb job (and I do think in this instance they'd try to do something about it even without the assaulted cyclist as a witness).