We all know how that worked with child sexual abuse cases - because the child was only one witness, unless the alleged perp confessed, he walked (and was even protected from cong. "gossip"!).
Would the same principle apply in a case of "fornication"? Say where a brother and a sister got a little "too close" and "did the nasty", unwitnessed by anyone else? If one confessed to the elders, but the other refused to admit anything, aren't they in the same boat as in child sexual abuse cases?