Liberty also whitewashed the anti-Semitism in the Labour Party, mind
Well, yes. One could be forgiven for observing that the former director of Liberty is today known as Baroness Chakrabarti CBE and is now part of Mr Corbyn's frontbench team as the Shadow Minister for Justice. This is an entirely unrelated coincidence, of course.
Anti-Semitism in the Labour party couldn't be discovered, because if they did then Labour would have to do something about it- which comes down to making a choice between firing the people involved or not.
If Labour did fire the anti-semities involved then they would lose important "alt-left" voices, and this would imperil the extreme left wing vote and potentially risk losing a certain large religious block vote that Labour has electorally positioned itself to represent, which happens to be institutionally anti-semitic.
If they do not fire those people, then they start losing a few of their "traditional" supporters and maybe their Jewish vote.
The number of people gained through keeping the anti-semities is smaller than those lost through firing them, so the obvious thing to do is what they are doing. Newspeak anti-semitism to mean something else, in order to keep the Jewish and traditional supporter vote onboard and hope it all blows over without them losing too many moderates.