What Happened to Kwan? (Possible Spoilers)

My real question was Who Killed Kwan (Sid's Father) but I had to change the title when I realized it was a spoiler. I'm kind of mystified! The way they held focus on the partial face and neck of the killer for a few seconds after he stabbed Kwan, tells me that we are supposed to know who killed him. I kind of thought it was the bodyguard of Stephen Ma, But the shape of the nose and mouth just didn't look right when I went back to check it. Did I miss something that the director was trying to tell us in his film shot of the killer after he stabbed Kwan?