Just by things players have said after playing the Pats. I remember Manning saying something about how he couldn't believe how they were never out of position and that it was like they were in the huddle with them after the AFC Championship game the year they held the Colts offense to 3 points which had been putting up over 30 a game all year.
Also, I remember a play during that game, where Bruschi ran straight at Rhodes on a screen play and arrived almost right at the time the ball did and stripped the ball. I was like, how in the hell did he know it would be a screen with that much confidence to go all out and run straight for Rhodes?
Lots of circumstantial evidence but, as we all know, that is all we will ever have after Goodell destroyed everything.