Harrison and George are best friends, they both live in Manchester.
One day, Harrison goes to George's house to visit him, but after opening the door, he finds his friend dead near the desk, with a hole in the head. There are many items on the desk, including a ream, a half-consumed pencil, an old-clock stuck at 9:03 and a cassette tape player with a cassette already in it. Harrison decides to listen the cassette, so he pushes the "Play" button. The audio isn't very clear, but he can distinguish a male voice speaking. Here's the message:
I'm George. I've just received a phone call, they said that somebody is coming now to kill me and he will be here within 2 minutes. I hear footsteps... someone is opening the door... oh no!
Harrison is shocked, but after thinking for a while, he realizes that the message wasn't recorded by George, but by his assassin!
How could Harrison know this?