Many Americans heard of a group called the Black Hebrew Israelites for the first time last week, when a member of their ranks shot up a kosher grocery in Jersey City, killing four. Having spent ten years in prison, I’ve frequently interacted with members of the Black Israelites , and I hardly need the Southern Poverty Law Center to tell me that they’re a hate group.I served my decade in upstate New York, guilty of amateur heroin-fueled armed robberies, living as a Jew in several congregations behind the walls of Maximum Security prisons. In four of them I was also the Rabbi’s clerk, and I was surprised to learn that, inside the New York State prison system, Jews make up seven percent of the inmate population, or more than three times their share of the population at large. For the most part, this is because all it takes to be recognized as a Jew in prison is submitting a “Change of Religion” form, after which the rabbi would note, always in Yiddish, on a prisoner’s personal file that the prisoner was “self-declared,” largely differentiating between those recognized as Jews by Halachic law and state regulations would open the door to discrimination lawsuits. However, because of the frequency of religion changes—usually timed to the benefits of being a Muslim at Ramadan and becoming a Jew for Rosh Hashanah—Albany limited the possibility of changing to once a year and not at all for those in solitary confinement.There were earnest men who wanted to convert to Judaism, men who learned Hebrew and studied the Torah. Unfortunately, it is impossible to do a halachic conversion in prison; one needs a mikvah bath to start. Most of the faux Jews “converted” for the kosher food, which was better; as a prisoner and a clerk, I understood their thinking and made a point of processing their papers quickly. But there were also the Black Hebrew Israelites who registered as Jews, and they were trouble.On many holidays, young Hasidic students would volunteer to visit prisons and bring cheer to the Jews on ice for Purim, say, wearing wigs and costumes, or lighting menorahs for Hanukkah or stopping by challah and honey on Rosh Hashanah. All the Jews in the facility were invited, which, sadly, meant that, for once, the Black Hebrew Israelites had a captive audience, rather than being one.Horribly embarrassing the rabbis and families of Jewish prisoners who could visit on these holidays, the Israelites would use these opportunities to aggressively claim the core tenet of their belief: That Jews as we know them are not Jews at all, and that the only real Jews are, of course, the Black Hebrew Israelites themselves.When the Black Israelites recite this hateful message in Times Square, say, using megaphones and wearing elaborate leather costumes, they often attack passersby with racial and particularly anti-Semitic rhetoric. On a busy Brooklyn street, I’ve personally heard them speak lovingly of gas chambers. But in prison, the Black Israelites were even more animated: They attacked the facility Rabbis, accusing them of being pretend Jews, denying their right to minister to any Jews and eating up the time we had for our rituals. Many of the guards were bewildered by the problems issuing from the usually mild-mannered group of religious Jewish prisoners, but in one facility, where a Jewish sergeant worked, the congregation was kept safe with the simple addition of a cop in a yarmulke who would end any disturbance as soon as it started by pulling out a pair of handcuffs. Nevertheless, the “self-declared” policy gave Israelites as much of a right to be there as Phil Drelich, Hasidic gabbai and double murderer. The Israelites insulted and terrified the old Jewish prisoners in yarmulkes and wheelchairs, and they often targeted me, shouting that I shouldn’t be allowed to serve as a rabbi’s assistant. Eventually, the Black Israelites were classed as their own group, separating them from the Jews. In some prisons, rabbis feared them so much that the Muslim Imams served as their chaplains.And so, while the Israelites’ black supremacy doesn’t fit the traditional media narrative of neo-Nazi thugs terrorizing Jews, we should guard against hate no matter where it comes from. If being in prison teaches you anything, it’s that you should be always vigilant; sadly, Jews everywhere should now internalize the same lesson.