Actually, just checked this, Liddel Hart does in fact say the following on page 685...
Peiper claimed at his post war trial that this was done in fulfilment of an order by Hitler that the thrust should be preceded "by a wave of terror".
I have a lot of respect for Liddel Hart's book, but in this case he seems at odds with others, such as Gordon Williamson. There used to be a substantial excerpt from Peiper's trial on this website, maybe the answer lies in there.
But I'd say Liddel Hart in this case was wrong.
And during the trial, Peiper blamed on himself to keep his men out of the troubles, to no avail. So, what do we do? Did he admit it? Did he not?
Oh, so embarrasing indeed.
By the way, I mean it was somewhat embarassing for the Allied prosecutors that a US order not to take prisoners was found but could find no order from the other side. it was not a remark on you.
Also, Peiper asked to have the weight of the sentence to be placed on him and not his men out of an old style sense of honour (that is sadly lacking these days). He never admitted guilt for any of the charges and in fact was nowhere near Malmedy when the shootings occured.