Well I can't help but disagree.
You say the police would have gone through the CCTV looking for Knox, Sollecito, Guede, Lumumba, Kercher et al. I totally agree. But wouldn't you say that NOT seeing any of those people on the CCTV footage where/when you would expect to see them if your narrative of the case was accurate would be.... rather significant? I would.
In this instance, the police/PM had a witness who stated she had heard a loud scream of terror, followed shortly afterwards by the sound of people running up the iron staircase by the car park. And the witness put the timing of these noises at around 11.00-11.45pm. The police had CCTV footage covering the iron staircase. Don't you think that it's a total slam-dunk that the police would/should have examined the CCTV footage to see whether they could a) corroborate Capezzali's account and b) potentially identify who - if anyone - was running up those iron stairs? I do.
And I also think that the police could/would have checked the CCTV footage for that entire evening. From 9pm to midnight. To see exactly who had (and who hadn't) gone up those stairs, who (if anyone) had run up those stairs, whether people had run up the stairs but outside Capezzali's timeline (at which point they could have at least tried to decide whether these were the people Capezzali must have heard, and that she must have been mistaken on the timing), and to try to identify all the people they saw going up those stairs.
And if the police did that - as I cannot believe they didn't do - then (if the brief allegation on the other website is accurate) they would have found that nobody ran up those steps later than 11pm that night. And that immediately calls into question Capezzali's timings and her credibility in general. I also had a working presumption that nobody was on that footage running up the stairs anywhere near 11pm (e.g. 10.45pm or even 10.15pm), since I can't believe the police wouldn't have pounced on that and altered Capezzali's timings accordingly.
I see what you say about it being easy to miss the significance of something that isn't there. But in this case, the police were using the account of Capezzali as part of their case. The police were effectively telling the court that Capezzali heard Kercher scream as she was murdered, and then heard more than one of her attackers run up the iron staircase. Capezzali's evidence was used to support the multiple-attacker theory, and the timing of the murder. So I contend that the police HAD to know that not seeing anyone running on that iron staircase later than 11pm that night was of extreme relevance.
To take the issue to extremes: imagine that there had been a CCTV camera covering the front door of the cottage, and that the police had the footage covering 10.30pm to midnight on the night of the murder. Imagine the police were saying (as they did indeed say) that Knox and Sollecito had arrived at the cottage at around 10.30pm, that they'd teamed up with Guede to kill Kercher, and that they'd left the cottage some time around 11.40pm. Would you suggest, in those circumstances, that it would be understandable for the police to "miss the significance of something that's not there" if they had examined the CCTV footage and had seen nobody enter or leave the cottage between 10.30pm and midnight?
The example is of course more extreme than that in respect of the iron staircase CCTV and Capezzali's account. But the underlying principle is exactly the same.