Although Williams finished with a productive 10.5-sack season, the Bills were lackluster as a team on the defensive side of the ball, giving up 362.9 total yards per game.
Following the season, the entire coaching staff was let go, including head coach Chan Gailey and defensive coordinator Dave Wannstedt.
This offseason, the Bills chose to go with former Syracuse head coach Doug Marrone as their new head coach. His choice for defensive coordinator was Mike Pettine.
Pettine will have his work cut out for him in Buffalo, trying to turn around a defense that was ranked 22nd in the league last season.
But Pettine is a good choice for the part. He has spent the last four seasons in the same role with the New York Jets, helping them have one of the league's better defensive units.
Although the Jets suffered a poor 2012 season, their defense was solid. In terms of total yards allowed per game, the Jets were No. 8 in the league.
Pettine will be able to bring this same style to Buffalo, where he has a great nucleus of young players at key positions.
Along with Williams, defensive linemen Marcell Dareus and Kyle Williams, cornerback Leodis McKelvin and safety Jairus Byrd are perennial All-Pros.
To go along with drafting linebacker Kiko Alonso out of Oregon, the Bills brought in some free agents who could be key contributors on defense in 2013.
Lawson has never had more than 68 tackles in a season, but he did have 6.5 sacks in the 2009 campaign. A former first-round selection of the San Francisco 49ers, Lawson is the type of player whom Pettine can get the most out of.
Pettine could use Lawson the same way he used David Harris in New York.
Harris is one of the most unheralded linebackers in the NFL, but he is all over the field. That is evidenced by the 123 tackles he had in 2012.
But it is the passing game where Pettine will likely have the biggest effect in Buffalo.
The Jets were No. 2 against the pass last season, and with McKelvin, Byrd and second-year cornerback Stephon Gilmore, Pettine could help build one of the league's best secondaries.
The Bills are headed in the right direction on offense and will be able to put points on the board with guys like C.J. Spiller, Steve Johnson and Robert Woods. If they can make some stops on defense, they could be dangerous.
While the Bills have a new head coach and two new quarterbacks heading into the 2013 season, their new defensive coordinator may be just as important as any of them.
The New England Patriots have won the AFC East nine out of the last 10 seasons, but the spot for their top-challenger within the division is there for the taking. Putting together a more aggressive, attacking defense is what the Bills need to do in order to take that spot and eventually overtake the Pats.
That is what Pettine has been tasked with, and he has the tools in place to get it done.