The First hint for the US was a car which goes to that abandoned house frequently. This car then goes away long miles to send and email and to make a telephone call. This was the thing which alerted US army.
Then the satellite was focused on that house. Once a man came out of that house and they was not sure that it was Osama.
They made a calculation. They first collection Osama’s height then they analyzed it with the photograph taken by the satellite. They calculated the angle of satellite and calculated the height of his shadow in the photo and time of the snap and the result gave more than 70% possibility that it was Osama.