He said he had obtained the television innocently, not knowing it had been stolen.

innocently 是形容词 innocent 的副词形式，innocent 意思是"无辜的、清白的"，加上 -ly 变成副词表示"以清白/无辜的方式"。 这里 innocently 修饰动词 obtain（获得），表示"以不知情/清白的方式获得"。