Complex sentence: There in Rome, they contacted the only person they knew, Jerome Paulin, an American scientist from the University of Georgia on sabbatical in Rome who had previously spent a sabbatical in Leningrad where he met Natasha Raikhel.
Split into simpler sentences: There in Rome, they contacted the only person they knew, Jerome Paulin, an American scientist from the University of Georgia on sabbatical in Rome. Paulin had previously spent a sabbatical in Leningrad where he met Natasha Raikhel.