He worked as a hairdresser in Whitechapel in the East End of London , where a series of murders ascribed to an unidentified person nicknamed "Jack the Ripper" were committed in From , Kosminski was institutionalised after he threatened his sister with a knife. Police officials from the time of the murders named one of their suspects as "Kosminski" the forename was not given , and described him as a Polish Jew in an insane asylum.
Almost a century after the final murder, the suspect "Kosminski" was identified as Aaron Kosminski; but there was little evidence to connect him with the "Kosminski" who was suspected of the murders, and their dates of death are different. In , he had bought a shawl which he believed to have been left at a murder scene and gave it to biochemist Jari Louhelainen to test for DNA. He emigrated from Poland in or , likely with his sisters' families.
The family initially lived in Germany. A nephew of his was born there in and a niece in It is not known precisely when Aaron left Poland to join his sisters or whether he lived in Germany for any length of time, although he may have left Poland as a result of the April pogroms following the assassination of Tsar Alexander II , the impetus for many other Jews to emigrate.
The family moved to Britain and settled in London sometime in or His mother, who was listed as a widow, apparently did not emigrate with the family immediately, but had joined them by It is unknown whether his father died or abandoned the family, but he did not emigrate to Britain with the rest of them. In London, Kosminski embarked on a career as a barber in Whitechapel , an impoverished slum in London's East End that had become home to many Jewish refugees who were fleeing economic hardship in Eastern Europe and pogroms in Tsarist Russia.
He possibly relied on his sisters' families for financial support, and may have lived with them at 3 Sion Square in and 16 Greenfield Street in , indicating that his sisters possibly shared responsibility for caring for him and he alternated living between their family homes. On 12 July , Kosminski was placed in Mile End Old Town workhouse due to his worsening mental illness, with his brother Woolf certifying the entry, and was released three days later.
