In October 1941, one of the largest single mass murders of Jewish people took place in Odessa, Transnistria (now Ukraine).

Romanian and German troops took the city on October 16. On the afternoon of October 22, a Soviet booby-trapped safe exploded inside the Romanian Military Headquarters killing the Romanian Commander and 66 others.

In retaliation, the Romanians led between 25,000 and 34,000 Jews out of town, tied them together in groups of 40–50 people, threw them into ditches and began to execute them. The Romanians decided that the killing was taking too long and was too expensive, so they led the remaining Jews into four large adjacent wooden warehouses. The doors were closed and the soldiers fired directly into the buildings through perforations they made in the walls.

In order to make sure that all the people inside the buildings had died, they poured gasoline into three of the buildings (one held women and children) and set them on fire. Those who tried to escape through windows or the roof were shot or met with hand grenades. On October 25, the fourth building, which was filled with men, was shelled.

Further Reading https://www.dw.com/en/the-odessa-massacre-remembering-the-holocaust-by-bullets/a-45844546

details, Odessa