What does God think of undercover cops?

I recently watched "The Departed" (excellent movie) and it made me wonder the above question. For those Christians that have seen the movie, Leonardo Dicaprio's character (an undercover cop) constantly lies throughout the film to protect his identity. However, his lies lead to the apprehension of many felons who would otherwise continue to kill, steal, extort, and sell arms to those who may use them for evil. I'm not saying that everything he did was correct, but could you say that he lied for good? That he was lying to protect the innocent and bring justice to the streets of Boston.