He does not realizes that the thief he is after is him, until the last episode where he makes correction to the portrait that looks strangely familiar then see his own reflection in a mirror in the mirror stall ,compares it to the corrected portrait then realizes it was him all along.

No, the story line was made known through him, and while he thinks he has caught a trace of the popular thief and he's going after him , he is actually the thief , he doesn't expect that he has become so popular, the poster going around doesn't look exactly like him, it is only a product of the unclear sightings his various victims as to what he should look like.

And while he's lost in his search for the thief blinded by the reward for catching him....