Let me clarify my question...
If an accusation was made by one person to the congregation they would not accept the word of a single witness.
If the alleged victim went to the police and they investigated, found the allegations to be true based on forensic evidence and prosecuted then this would be accepted as a second witness and judicial action taken.
I believe this is the case but I can't recall where I have seen this documented and could be wrong.
They also treat another allegation by another person as a second witness but this has been a change made to policy over time.
Of course, the historical problem has always been that the allegations are made firstly to the elders. They don't take action and no report to the authorities is made so nothing happens.
It all boils down the the WT approach on being proactive. The simple thing would be to ensure any allegation gets reported which puts the onus on the authorities to access the risks, investigate and protect the victim. They can then await the outcome of the secular process to determine if the "scriptural" parameters are met.
Instead they want to limit their response as far as possible. They only report when they legally have to. They are not proactive in ensuring the authorities are involved. Instead of co-operating with the authorities and implementing change they tweak the processes to make things appear better but do nothing to change the cultural norms endemic to the organisation of a patriarchal, top down, controlling environment.