Complex sentence: Gordon, West and Rita arrive at the scene and find the dying McGrath, who then explains that Loveless the one behind one of McGrath's past crimes: a tank massacre of a settlement called New Liberty inhabited by freed slaves, including West's family.
Split into simpler sentences: Gordon, West and Rita arrive at the scene and find the dying McGrath. West then learns Loveless is the one behind one of McGrath's past crimes: a tank massacre of a settlement of free slaves, including West's family.