I'd give more credibility and weight to physical evidence than a witness statement any day.
Trouble is you are having to rely on assumptions made from that evidence.
In a crash, you might hear that the nearside front tyre of the car deflated.
It did, that's unarguable.
What you then hear is the damage investigator's opinion of what that means - that's when it gets difficult.
As I said, a lot of these guys are very clever.
But equally, I've been to hearings at which two apparently equally qualified experts give conflicting evidence.
It's then for a jury if there is one, or the coroner when sitting alone, to weigh up which interpretation of the events is the most likely.