he was conscious while he was committing.是正确的.
句中“作案的时候”是一个较精确的时间状语,故用过去进行时,不用一般过去时.至于用when还是while在这里是一样的,美国人用while多.
注意：when he commiting是不可能的,这是初中的错误水平,当逻辑主语一致时when he was commiting中he was 可同时去掉,写成when commiting,太重要的知识点了.