Were caught filming other teams' practices
Have multiple people saying they bugged the visiting teams' locker rooms and taking playbooks
*allegedly* deflating footballs for a competitive advantage

And those are just the three that made headlines. Maybe all NFL teams cheat, but one rises well above the others and that's pretty clear. Is that why they have dominated the last 15 years? Nope. Belichek and Brady are amazing. Only Pops and Duncan compare. But it may have helped them win a game or two along the way and in my mind it taints everything they've accomplished. Deny all you want.