The same way you prove any negative - by proving it can't be anything else.
That's why prisons have video cameras and the guards don't sleep at their post, so if somebody dies you know nobody else went into their cell and did it to them. Couldn't have been anything but a suicide.
In this case the cameras were out and the guards asleep, so 'unfortunately' nobody can know for sure what actually happened.
How do you ever get "prove" a suicide as a cause of death?
It's like trying to prove a negative.
I'm sure autopsies and coroner's reports can make educated guesses, but suicide is more of a motive than an objective finding.
The same way you prove any negative - by proving it can't be anything else.
That's why prisons have video cameras and the guards don't sleep at their post, so if somebody dies you know nobody else went into their cell and did it to them. Couldn't have been anything but a suicide.
In this case the cameras were out and the guards asleep, so 'unfortunately' nobody can know for sure what actually happened.