"If brutal killers like these two are at work, it is no wonder that so many people have fled," he said.

no 在这里表示否定，意思是"没有"。 wonder 是名词，意思是"惊奇、惊讶"或"奇迹"。 no wonder 是一个固定短语，意思是"难怪、不足为奇"，表示对某事的发生不感到惊讶。