One of the signatories of the "Jerusalem Declaration on Antisemitism" praised a book claiming Jews might have really killed Christian children for matzoh

In 2007, a huge controversy erupted over the publication of a book in Italian, Bloody Passovers: The Jews of Europe and Ritual Murders, by Ariel Toaff. The book argued that it might be true that in some cases, Jews may have really engaged in ritual slaughter of Christian children - even for use in Passover matzoh. 

Toaff's main scholarship seems to have been to reveal that some Ashkenazic rabbis allowed the use of dried blood as an ingredient for medicines that Christians used as well  - blood that came from willing, living donors. He goes beyond that to speculate, based on very dubious theories, that some extremist Jewish sects may have used this powder in Passover ceremonies.

The 3000 copies of the book were sold out immediately, but at the time hardly anyone actually read it. The book was ripped apart by most historians as a poor example of research, elevating hints and unreliable sources as proofs and accepting the testimonies of Jews under torture as proof.

He moves from one source to another, in a cavalier fashion, “going back to the Trent trial and moving on to the events in Norwich, to an iconographic study of sixteenth century haggadoth and to the rituals associated with the Seder, to end with the sad and grotesque adventure of a German Jew, a painter of miniatures, implicated by pure chance in the events at Trent.”49 Toaff’s style is lively, reminiscent of tabloid sensationalism. Readers may find themselves agreeing with the accusers as the author goes out of his way to address himself to “a public accustomed to screen violence in the movies. ... Readers of Toaff’s story encounter colorful protagonists whose psychology is simple: ‘Jewish adventurers engaged in illegal dealings,’ ‘a clever physician from Candia,’ ‘a strange young painter,’ a German rabbi who performs circumcisions (the Cutter!), ‘Jewish children handed over to the dangerous blade of his knife.’ And, why not, cannibalism, leprosy, suicide, buckets of blood.”50 Toaff erases the distinction between true and false. “This book is a tragedy. It is filled with half truths, a mixture of testimonies and points of view that are not believable. The way in which this book is written encourages the non specialist reader to reach conclusions of a very serious nature.”51

However, one historian praised the book. 

Two days before publication, Sergio Luzzato wrote a full page review in Corriere della Sera where he says that “in a large region where German was spoken, between the Rhine, the Danube and the Adige, some Jews really performed human sacrifices several times.” Luzzatto calls Toaff’s book as "magnificent history." He says Toaff "displays an extraordinary mastery in the fields of history, theology and anthropology.” He praises Toaff's bravery: "After the tragedy of the Shoah, it is understandable that the blood libel should have become a taboo topic. Further, that it had become the clearest proof, not of the perfidy of the accused, but of the judges’ racism. Today only an act of unheard of intellectual courage could have led to the reopening of the case. The starting point of the investigation is a question as precise as it is delicate: when the question of the crucifixion of children on the eve of Passover and the mixing of their blood in the making of matzot comes up, are we talking of myths, of ancient and ideological beliefs, or are we talking about rituals, that is to say, real events, prescribed by the rabbis? Now this question has been courageously answered.”

As bad as Toaff's actual book was, Luzzato's review misrepresented it to imply that it said things beyond what Toaff actually wrote. 

Two weeks later, Luzzato doubled down in that same newspaper, saying that testimonies of Jews under torture does not automatically make their words untrue.

In many ways, Luzzato was the main person responsible for the revival of the blood libel in the 21st century. His review and later article gave fuel to antisemites, elevating a poorly researched book that probably would have sunk into obscurity without him and promoting the blood libel as potentially being true.

Luzzatto is one of the signatories of the "Jerusalem Declaration on Antisemitism." 

Someone who doesn't seem to even understand his role in antisemitism, and who even promoted the most vicious example of antisemitism in the Middle Ages, is endorsing a definition of antisemitism that is embraced by other antisemites. 

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