Which tvb series is this?

I'm looking for the name of a tvb series. It's a mystery type series where one of the last cases is where this police (i think is bobby au yeung) is trapped in a box trailer by this guy. The guy who trapped him has scars all over his face and is doing this for revenge for this girl. I also remember that he works as a clown in a mall and got the police's fingerprint by having him hold a plastic cup. Please help, i am desperartley looking for the name of this series!

*its tvb as in television broadcast, a chinese channel*