首先来分析一下错句：Anyone did this must be caught...must be caught是谓语部分，根据本句的含义，主语应该是anyone， did this修饰anyone做定语，本句错误点是定语从句少了关系代词，也就是定语从句的引导词。改成Anyone who/ that did this must be caught.另外，提问者要注意的是anyone did this 是一个简单句，首先不管句意是否正确，从句子成分上来说，简单句不能做句子成分，而是从句才可以充当句子成分。