Matthew: "In itself it may not be but you've got to ask why a report from a delegation of Northern Irish trade unionists to Israel/Palestine in 2011 mentions it if it is not to whip up general hostilty to Israeli Jews by evoking mediaeval anti-semitic images."
That's not so much answering the question posed above as simply repeating Eric Lee's point again. And it appears to contain quite an assumption: that to even mention such reports is, in Eric Lee's words, to adopt "traditional anti-semitic images and messages". But the key issue, obviously, is what evidence there is to suggest that the incident actually happened. All that Lee has to say on this point is that "the report neglects to mention that no one was actually arrested, let alone convicted, of this crime." Is this intended as a criticism of the Israeli authorities for not taking such matters seriously, or is it implying that if a racially motivated crime doesn't lead to arrest or conviction, it must never have happened? As far as I'm aware (or have read online), the murder did happen. (I would happily stand corrected if someone provided further info. on it.) It's not good enough to simply assume (if anybody is) that because the "ritualistic" elements sound similar to anti-Semitic myths that they probably never happened, or should never be spoken of because they appear like anti-Semitic myths. Would Workers Liberty take the same approach towards reports of alleged crimes by Islamic fundamentalists if those reports happened to coincide with "medieval" stereotypes about Muslims?
As for why the Irish Congress of Trade Unions may wish to resurrect such matters, I haven't read the report so I don't know the context in which the quote appeared, but it is well known that the violent behaviour of some settlers is driven partially by the deeply reactionary strain of (fundamentalist) Judaism to which they subscribe. Given that the settlements themselves only exist on the basis of the Israeli state's awesome military power, I'd say it was pretty obvious why the Israeli ruling class bears responsibility and should therefore become the focus of criticism by socialists and trade unionists if such incidents take place -- especially when no arrests or convictions follow. As an example of racially/religiously motivated hatred, by settlers whose status and territory is defended and whose ideology and actions are tolerated by the Israeli authorities, it stands as a particularly brutal example of what the occupation entails. If it overlaps in any way with anti-Semitic myths, we shouldn't hesitate to distance ourselves from those who wish to appropriate such crimes for an anti-Semitic purposes, while pointing out that it is not necessarily anti-Semitic to raise such matters and condemn them.
Throwing accusations of anti-Semitism around is never helpful and smacks of petty moral/political point-scoring. Ironically, the position on anti-Semitism promoted by articles like this is almost identical to the SWP's position on Islamophobia, which is to make it so wide-ranging and all-encompassing as to be practically applicable to everything, regardless of context.