Complex sentence: A number of Chechens deemed to be collaborators were rounded up, detained, and executed; reliable sources have stated that the execution list for one region of Grozny comprised more than 200 names.
Split into simpler sentences: A number of Chechens deemed to be collaborators were rounded up, detained, and executed. Reliable sources stated that the execution list for one region of Grozny comprised more than 200 names.