7. The Homeless Network
Whatever "I owe you" meant , from the complicated to the extremely simple, the theory is that Sherlock knew what was going to happen in advance, so he planned for the Reichenbach Fall. Let's go back to that fall though, and look at another theory of how he did it... The Homeless Network were first introduced in 'The Great Game', as Sherlock's eyes and ears of the city, and later mentioned in 'A Scandal in Belgravia'. What if they were the ones that gathered round him, and swapped the body? What if they were there simply to stop John from getting too close to the crime scene? Look at the way they push him away; it's more than possible that if you were a passer-by that had just seen a man throw himself off a building, you'd stop a fellow passer-by from getting too close, especially if he was a bit dazed and confused. But don't these people look too organised? The nurse aside, obviously. As Sherlock landed, the crowd gathered. If that happened on my street, I think it'd be more a scene of people phoning for help, comforting those in shock of witnessing it. These passers-by however, gather round the body. If it's not the homeless network, it's a very organised general public.