Assuming the Gospels are eye-witness accounts, how were certain events recorded where Jesus was alone? For instance, the temptation in the desert. It was only Jesus and Satan there. Who could have recorded that?

Or the prayers of Jesus in the garden of Gethsemane? Jesus went up alone while the disciples slept. Who could have recorded the words He spoke there as an eye witness?
Using Occam's razor, there is no reason to expect a supernatural medium for the transmission of this information to the disciples. Jesus spent three years with his disciples. They had plenty of time to sit around the campfire, telling stories.