That is important to remember but it is sort of orthogonal to the point being made. Assuming that mind-reading worked perfectly you can find the truth about what the person believes. In most cases if they think they murdered the person and the gun is hidden behind the oak in their backyard it is beyond a reasonable doubt. I think it is still useful to have the truth about what that person believes, even if we have to remember that their beliefs are fallible.
That is important to remember but it is sort of orthogonal to the point being made. Assuming that mind-reading worked perfectly you can find the truth about what the person believes. In most cases if they think they murdered the person and the gun is hidden behind the oak in their backyard it is beyond a reasonable doubt. I think it is still useful to have the truth about what that person believes, even if we have to remember that their beliefs are fallible.