You should read the following articles. Belicheat is simply a dishonest and dishonorable coach. I think he is lower than Pete rose. Because of his cheating, guys like Brady and Gronkowski are way over rated. When you know what the defense is doing on most plays, it makes the game easier.
https://nypost.com/2015/09/08/spygate-much-worse-than-belichick-goodell-divulged-report/
http://www.espn.com/espn/otl/story/_/id/13533995/split-nfl-new-england-patriots-apart
http://profootballtalk.nbcsports.com/2015/09/11/at-least-five-teams-have-suspected-patriots-of-headset-tampering/
https://www.si.com/nfl/2015/09/08/patriots-cheating-suspicions-bill-belichick-tom-brady