I came across this article, The Alexandrian Riots of 38 C.E. and the Persecution of the Jews: A Historical Reconstruction. By Sandra Gambetti in the Journal for the Study of Judaism and went searching.
She's published a book and the blurb:
Scholars have read the Alexandrian riots of 38 CE according to intertwined dichotomies. The Alexandrian Jews fought to keep their citizenship - or to acquire it; they evaded the payment of the poll-tax - or prevented any attempts to impose it on them; they safeguarded their identity against the Greeks - or against the Egyptians. Avoiding that pattern and building on the historical reconstruction of the experience of the Alexandrian Jewish community under the Ptolemies, this work submits that the riots were the legal and political consequence of an imperial adjudication against the Jews. Most of the Jews lost their residence never to recover it again. The Roman emperor, the Roman prefect of Egypt and the Alexandrian citizenry - all shared responsibilities according to their respective and expected roles.
From a book review by Torrey Seland::
..she argues that the Jews were not expelled from Alexandria as such but secluded into a small part of it labeled the Delta District (Δ)...
... Gambetti takes as her point of departure the summer of 38, when the Alexandrian Jews were pushed back into the Δ section of the city, which suggests that the problem was not the Jews qua Jews, but where they lived. Chapter Two (pp. 23-55) deals with the rights of residence of the Jews in the Ptolemaic times. She argues, inter alia, that at that time the Jews had their own politeuma, but it was limited to the territory of their garrison...Chapter Four (77-85) deals with the early years of Flaccus’ prefecture. Gambetti argues that Flaccus did not favor the Jews, though his policy remains unclear in many aspects. That he did not deliver the Jewish decree to the emperor was more due to the difficult situation of Flaccus’ own situation than his reluctance to deliver it.
The fifth chapter, The Precedent for the Riots (pp. 87-136), which is central to Gambetti’s argument, presents her reading of P. Yale II 107. The main conclusion of her discussion is that this papyrus deals with a conflict between two groups opposing each other before Gaius, the Emperor; the one party was the Alexandrians, the other was composed of Alexandrian Jews. The case before Gaius is dated to March 37, possibly in Rome. But the two groups, which in fact were delegations, had left Alexandria as early as about August 35. According to Gambetti’s reading, the Jews seem to have lost their case...the danger of losing one’s patris. Gambetti’s conclusion, important for her whole study, is that the accuser and supplicants – mentioned in this papyrus – were Jews, and that they lost their case: “The reason for this loss was residence; the representative of the Jews apparently registered his idia in a mistaken part of the city; his guilt extended to the whole group” (p.136).
The following three chapters (pp. 137-193) deal with the events of 38 CE:...When it comes to the events of the riot in 38, Gambetti suggests that they were primarily due not to the ‘mob’ (contra Philo), but to political leaders of some sort (p.171), most probably the leaders of the gymnasium. Furthermore, the famous edict of Flaccus, declaring the Jews to be “foreigners and immigrants” in the city, Gambetti reads to denote not all Jews but primarily the Jews living outside their designated area, that is outside the Δ district...Gambetti discusses here the old Egyptian enmity against the Jews as a possible factor. In dealing with the cultural and demographic aspects of the riots, she focuses on the roles of the professional and religious associations in the city. Then, in the final main chapter (pp. 213-238), the author deals with the years 39 and 41...
Highly recommended for anyone interested in the situation of the Jewish community in antiquity.
But what actually happened to the Jews? The background is here. And, according to one account:
...the Jews were trapped. They had been living in all five quarters of the city; now they were ordered to live in one part, close together. It may be that Flaccus thought that this segregation would help the Jews, because it now became impossible to attack them as individuals. Whatever the motive, the result was the first known ghetto in history. Of course, the houses the Jews had left, were plundered by the Egyptian and Greek mob.
It was impossible for the Jews to leave their quarter: they were stoned, clubbed, or burned and the dead bodies were mutilated. Others were brought to the arena or crucified. Philo gives a shocking eyewitness account. Thousands must have perished, and -according to Philo- Flaccus did nothing to prevent it; instead, he sided with the attackers. Members of the Jewish council were arrested and whipped in the theater to celebrate the birthday of the emperor; others were crucified (31 August, a sabbath).
After this, the situation seems to have relaxed a bit: as long as they stayed in their ghetto, the Jews were more or less save; the governor had shown the Greeks that he was one of them, and it is possible that he now had the credit to persuade the mob to calm down. It was a cynical solution, but the killing may have ceased.