Emanuel Ringleblum dedicated significant part of his journal (published as Kronika getta warszawskiego in Polish, English translation published as Notes From The Warsaw Ghetto). Many parts of his journal describes brutality of the Jewish Ghetto Police:
February 27th (...) a young Jew was killed by the Jewish Law and Order Service. He struck a Jewish policeman and was executed in the Jewish Council building.
End of March (...) The avarice of the Jewish police is such that they take 20 groschen from smuggler boys for every loaf of smuggled bread.—
May 11th (...) The Jewish police uses the principle of collective responsibility, imitating the Germans. They close the gates of courtyards because all the tenants have not paid the police tax—30 groschen per capita. They take members of the House Committee as hostages if one of the tenants in a particular courtyard doesn’t present himself for forced labor service at a camp.
July 11th (...)Another factor in keeping the populace in check is the Jewish police who have learned how to beat up people, how to “keep order,” how to send folk to work camps.
especially during the liquidation of the Ghetto:
The Jewish police had a very bad name even before the resettlement. The Polish police didn’t take part in the forced work press gangs, but the Jewish police engaged in that ugly business. Jewish policemen also distinguished themselves with their fearful corruption and immorality. But they reached the height of viciousness during the resettlement. They said not a single word of protest against this revolting assignment to lead their own brothers to the slaughter. The police were psychologically prepared for the dirty work and executed it thoroughly.
How could Jews have dragged women and children, the old and the sick, to the wagons—knowing they were all being driven to the slaughter?
In the presence of such nihilism, apparent in the whole gamut of our society, from the highest to the lowest, it is no surprise that the Jewish police executed the German resettlement orders with the greatest of zeal. And yet the fact remains that most of the time during the resettlement operation the Jewish police exceeded their daily quotas. That meant they were preparing a reserve for the next day. No sign of sorrow or pain appeared on the faces of the policemen. On the contrary, one saw satisfied and happy individuals, well fed, loaded with the loot they carried off in company with the Ukrainian guards.
Very often, the cruelty of the Jewish police exceeded that of the Germans, Ukrainians, and Letts. They uncovered more than one hiding place, aiming to be plus catholique que le pope and so curry favor with the Occupying Power. Victims who succeeded in escaping the German eye were picked up by the Jewish police.
Beside the police, another group of organizations shared in the resettlement operation. Gancwajch’s redcapped Special Ambulance Service was the worst. (...) Besides, a Special Service uniform enabled its wearer to perpetrate a variety of swindles and blackmail associated with sanitation (informing on typhus cases, disinfection steam baths, and the like). It was this pretty gang that now voluntarily reported for the assignment of sending Jews to the hereafter—and they distinguished themselves with their brutality and inhumanity. Their caps were covered with the bloodstains of the Jewish people.
The officials of the Jewish Council also cooperated in the "operation", as did the Service of the K.A.M.—City Aid Committee.
He also comments on activity of Abraham Gancwajch and the Group 13, and overall corruption, extortion and blackmail.
The history of The Łódź Ghetto (the second-largest ghetto (...) after the Warsaw Ghetto), with it head of Council, Chaim Rumkowski, described by Ringleblum:
Lodz, Chaim, or, as he is called, “King Chaim,” Rumkowski, an old man of seventy, extraordinarily ambitious and pretty nutty. He recited the marvels of his Ghetto. He has a Jewish kingdom there, with 400 policemen, three jails. He has a foreign ministry, and all the other ministries, too. When asked why, if things were so good there, the mortality is so high, he did not answer. He considers himself God’s anointed.
Rumkowski, were actively involved in extortion, sending his opponents to concentration camps ans sexual abuse and ultimately died of hands of Jewish Sonderkommando inmates who beat him to death as revenge for his role in the Holocaust.
While his role in the Holocaust is a matter of dispute, it is worth noting that Łódź Ghetto survived almost two significantly longer than any other ghetto, although Ringleblum note:
In connection with the visit of Rumkowsla, it is worth noting that three-quarters of a year ago, when a German commission visited Lodz, he represented the Lodz Ghetto as a paradise. This was said to have influenced the establishment of ghettos in other cities of the Government General of Poland. That is to say, Rumkowski proved that the Ghetto experiment was a success.
is likely an exaggeration.
All quotes from Notes From The Warsaw Ghetto: The Journal Of Emmanuel Ringelblum, Pickle Partners Publishing, 2015.