At 53 mins the detective takes a photo of highlighted text in an open book. As the camera angle changes, the book is now closed despite him still holding up the phone as he's just taken the photo.
(at around 25 mins) When the detectives enter the crime scene at the children's park, there is a mirror as a part of the playground. When one of the detectives moves to reveal the mirror, you can see what appears to be a crew member holding a boom mic.