Does joking about it in texts prove that they were a) actually doing it, and b) if they were deflating balls, do the texts prove that they were deflating them below legal levels?
When you combine that with multiple teams in the league suspecting and reporting that’s what the Pats were doing, with the very “Deflator” the one who took the balls from the officials office into the locked restroom—and that the balls were significantly deflated after that point, you have a pretty good circumstantial case.
A circumstantial case is what just locked ex-Pat Aaron Hernandez away for life.
And NFL discipline has a significantly lower standard to be met than does a murder trial.