Complex sentence: The fugitives included two Poles, a Latvian, a Lithuanian, a Czech and an enigmatic US engineer called "Mr. Smith"; they were later joined by a 17-year-old Polish girl.
Split into simpler sentences: The fugitives included 2 Poles, a Latvian, a Lithuanian, a Czech and an enigmatic US engineer called "Mr. Smith". They were later joined by another fugitive, a 17-year-old Polish girl.