Is the climax of "The Tell-Tale Heart" when the narrator kills the old man, or when his deed is discovered?

Hearing the old man's heartbeat beating unusually and dangerously quick from terror, the narrator decides to strike, jumping out with a loud yell giving the old man a heart attack and then smothering the old man with his own bed. The narrator proceeds to chop up the body and conceal the pieces under the floorboards. The narrator makes certain to hide all signs of the crime. Even so, the old man's scream during the night causes a neighbor to call the police.