the refutation of the Blood Libel that answers all questions.

where bodies turn up someone killed them. That it was Jews is another matter. That it was done by people who could pass as Jews is obvious.
Harranians are a better candidate, here's why.

The Harranian cult, coherent to ancient Mesopotamian cults, was doing human sacrifice semi secretly into islamic times, and finally shut down by the Mongol invasion of Syria. It was also the source for hermeticism transferred from the ancient world into arabic and Renaissance learning. Among alchemists there were a few who did human sacrifice, and two such turned Gilles de Rais onto this.
Initially, the Harranians deceived the moslems into thinking they were the sabians mentioned in the koran. (given the demonic origins of the koran, they probably were.) So they could go on dhimmi status instead of convert or die. Thus deception about their faith was endemic for centuries after that.

The style of killing (until AFTER the closet satanist Jacob Frank got into the game) was not kosher. Blood is absolutely forbidden to be ingested. Humans are an unclean animal because we don't chew the cud or split the foot. The picture of use of this in Passover matzoh is exactly comparable to satanist black mass desecration of the host in a Roman Catholic context, this ritual murder stuff is sacrilege in a Jewish context, which probaby originated as diaspora Harranians doing their thing, and pretending to be Jews, and many families may have lost the next generations to Judaism, the kids having seriously devoted themselves to Judaism they were raised in, before old enough to be told the truth. Ditto phenomenon among those Harranian families who passed themselves as exotic looking europeans who were into philosophy and so forth, which would have a Christian outer layer, and many younger generation may have become too Christian to admit to the family secret. Probably in any generation, remaining Harranians could fit in one room.

The style of Harranian kills is not known, or I haven't found it yet. The first reference to this puncture exsanguination style, was regarding some sect of the Montanist Christian heretics. Not the usual scene with them, but I suspect Harranians got into it.

Where philosophy abounded, so did magic. Both would have gone into Europe and elsewhere with the Harranians.

Because of the tiny number each generation that could be told the family secret, they would always be a tiny element.

Fast Forward to the 20th century, in the USA, where no one had to pretend to be anything, they could revert to their original paganism semi openly and some could do the kills in the old way.

Hence the reversion to the multi puncture type kill in AD 1955.

Since satanists have always gravitated to positions of power, incl. local, and would have been in position to stop an inquiry, especially if the Harranians responsible were also in the police and higher up in Chicago, an ethnic melting pot no one would notice them in, the cover up is explainable. Jews would not have wanted a blood libel dragged up and riots, Harranians would not want an investigation even though it might target Jews, it is likely that one of those in the act itself was still passing as Jewish or considered such because of heavy identification with the Kabbalah, or because of the latter preferred to be viewed as Jewish, ergo the picture of a pay off by Jews and a suppression by the authorities.

the date on all this means that likely if the original perpetrators are dead or senile, at least a few of their children or grandchildren are alive and kicking....and involved in satanism of the ancient Mesopotamian paganism influenced sort.