The employee being released I understand. Connection with Brady is all inference. Which, as you say, is enough in some cases with other evidence. However, the two employees they interviewed denied a scheme under oath, despite losing their jobs. Brady has denied it under oath.

And they do not have compelling evidence of the underlying crime. Natural physical forces could produce the pressure drop they measured.

To draw any other conclusion would require far more stringent procedures that the NFL did not possess (including a log of the original inflation pressure) at the time. This process is ludicrous.