A coroner has apologised for being unable to offer a father an explanation for the death of his son.
Durham coroner Andrew Tweddle was speaking at the conclusion of an inquest into the death of 22-year-old motorcyclist Michael Laidler, who died of head injuries when he crashed into a wall on a minor road south of the C77 road between Rookhope and Ireshopeburn in August.
An inquest at Crook Coroner's Court heard Michael, of West Rainton, had been out for a ride with his brother David, but David had been in front and had not seen what happened.
The pair were experienced and Michael was wearing a regulation helmet and riding a bike that was well capable of handling the road conditions.
Accident investigator PC Paul Harris told the hearing it was not possible to say why Michael had lost control but he believed he had been travelling no faster than 30-40mph.
"I would not believe that to be excessive," he said.
"I am not a motorcyclist myself but I think, on that type of bike, I would be quite comfortable riding along there at that type of speed."
Michael was diabetic and Mr Tweddle said his condition had been taken into account as a possible explanation of what happened.
Blood tests had been inconclusive but a pathologist had concluded diabetes was unlikely to have been a factor, given Michael's medical history.
Recording a verdict that Michael died in a road accident, Mr Tweddle said it was his role to explain what had caused the crash but had he had been unable to do so.
"That is what I am here for, to get that information, to share it with the family," he said.
"But unfortunately I am no wiser than I was when the inquest started with trying to understand why someone like Michael, who was experienced and riding a bike like this on this type of road, why he would have lost control.
"If the police officer had said he was doing 100mph along there, it might have been easier to understand - there is certainly no indication he was driving too fast for that type of environment."
He told Michael's father Trevor: "Speed does not seem to be a factor, which makes it even more difficult clearly to understand what went wrong - I just do not know.
"That is for unfortunate from my point of view and I am sure it is from yours. Despite the thoroughness of the investigation, I do not have an answer as to why what happened did happen, and I am sorry for that.
"I really do not know why Michael lost control of the bike in the way he did, when he did. It will remain unknown and to guess would be just that because there is no evidence I can find that would help me answer that question."
Speaking after the hearing, Mr Laidler said: "We have lost him, whatever the reason was.
"We can just be assured that he was not doing being stupid."