Simplify the following text for a Grade 12 native English-speaking person.
Original: Shocked by the constant beating of the heart and a feeling that not only are the officers aware of the sound , but that they also suspect him , the narrator confesses to killing the old man and tells them to tear up the floorboards to reveal the body .
Simplified: Shocked by the constant beating of the heart and a feeling that the officers must be aware of the heartbeats , the narrator loses control and confesses to killing the old man and tells them to tear up the floorboards to reveal the body .