When Claire is speaking to the second-hand goods store owner, a group of people in the background turn to look at the camera, then they start smiling and looking back and forth between each other and the camera, obviously noticing that they're being filmed.
The officer who sees the scene with Luther (a homeless man) trying to resuscitate Gwen George, the episode's murder victim, actually couldn't have "seen" it. The police car he was riding in was still half a block away from the alleyway and there would have been no way to have noticed anything down the alley from an angle.