The rider might have offered his services as a witness, although given that at least one driver was intent on blaming him, it might have ended up as more hassle than it's worth. I once saw a driver rear-ending another on the Lea Bridge Road and stopped, explaining that I'd seen it and could be a witness. They both looked at me rather confusedly and said that they'd just swap insurance details and all was fine. As fault is quite clearly apportioned in cases of rear-end crashes, I suspect that in this case, too, it probably wasn't necessary to offer to be a witness.
The rider might have offered his services as a witness, although given that at least one driver was intent on blaming him, it might have ended up as more hassle than it's worth. I once saw a driver rear-ending another on the Lea Bridge Road and stopped, explaining that I'd seen it and could be a witness. They both looked at me rather confusedly and said that they'd just swap insurance details and all was fine. As fault is quite clearly apportioned in cases of rear-end crashes, I suspect that in this case, too, it probably wasn't necessary to offer to be a witness.