The Jewish cemetery in Rome has been forcibly relocated at least twice, in the past four hundred years. 
These remains go back to when the cemetery was situated in the Trastevere area, and presumably they had been overlooked when the cemetery was moved before.
The intriguing reference to the 'Company of Death' turns out to be an abbreviation for the 'Compagnia della Morte degli Ebrei' - which was the organisation which managed and operated the Jewish cemetery.