[Well, he's not going to just leave a situation alone. But he doesn't want to be the police, either. He's comfortable being an intermediary. Someone who helps the police, works under their auspices, but isn't actually in charge of what to do with the criminals after they're captured. The catching is the part that he's good at... most of the time.

He wishes Sherlock were here.]

I can't just leave something alone, Mr. Solomons. [Get that out of the way.] If that means I have to choose to play police in your eyes, then I guess that's where we are.

[He doesn't sound happy about that at all. In fact, he sounds entirely reluctant. John isn't going to argue about definitions with the other man at the moment, though.]