Sandra Bullock is not very convincing as a tough cop, but she does a better job than Jennifer Lopez in Angel Eyes. The two films have a lot of similarities (and they're both bad).
The movie does quite a good job with the two villains, Richard Haywood (Ryan Goslin) and Justin Pendleton (Michael Pitt) who showcase what it means to be manipulated. While one's a theoretical cold blooded killer, the other is the same in real life. There's a lot of homosexual undertones to their relationship which doesn't make sense but seems to be thrown in there because it's "cool". The two killers devise "perfect murder" schemes to kill young girls and have someone else take the fall. This works until there is friction between the two of them and they have to deal with each other.
Bullock not only has to bring down the killers, but she must also confront her own demons, having to do with an abusive relationship. This kind of cliched story is why Murder by Numbers is worth checking out only if all other options have been exhausted.