The two players were among the Bills' most experienced defenders, and finished first and second on the team in tackles last season. And yet, they were also part of a high-priced defense that finished among the NFL's worst in yards and points allowed.
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"Moves like the ones we've made today are never easy, but we have to do what's best for our team and keep moving forward," general manager Buddy Nix said in a statement released by the team. "We've got some good young players on our roster, who we feel are ready to take the next step up. And they will now have the opportunity to do so."
The Bills are in transition once again after Marrone was hired last month to replace Chan Gailey, who was fired after three consecutive losing seasons. Marrone, the former Syracuse coach, has brought in an entirely new staff, including luring New York Jets defensive coordinator Mike Pettine to take over the same role in Buffalo.
In a separate development, veteran defensive end Chris Kelsay is ready to return after a partially torn ligament in his neck forced him to finish last season on injured reserve. Kelsay, who missed the final five games last season, told The Associated Press on Monday that he has fully recovered from the injury after being examined by the Bills' doctors last month.
Barnett is a 10-year NFL veteran, who never missed a start in his two seasons in Buffalo after signing with the team in free agency. He led the Bills last season with 112 tackles while adding two sacks.
Barnett beat the Bills in releasing the news by announcing he was going to be cut on his Twitter account early Monday afternoon.
"Thanks to all the great fans and friends I have met in Western New York. It was truly a pleasure being apart (sic) of that organization and culture," Barnett wrote. "Very unfortunate we didn't get the Bills to the playoffs but I know you guys will have many successful years ahead of you. ... Sad to leave but like they say when one door closes more open up."
The Bills signed Barnett after losing Paul Posluszny to free agency shortly after the NFL lockout ended in July 2011. Barnett spent his first eight seasons with Green Bay. He was entering the final year of his contract in Buffalo, and due to make a $3.5 million base salary.
The Bills are already thin at linebacker, making the position a priority in free agency and the draft in the coming months.
Wilson was highly regarded for his work ethic and resilience. He broke in with the Bills as a receiver in 2005 before being converted into a safety while spending the 2006 season on the team's practice squad. He made an immediate impact at his new spot in 2007, when Wilson started nine games and had two interceptions, both of which he returned for touchdowns.
Last season, Wilson finished second on the team with 98 tackles but no interceptions. Most notably, he had two potential fourth-quarter interceptions drop from his hands in losses to Tennessee and St. Louis -- both decided in the final minutes.
Wilson was also entering the final year of his contract, and due to make a $2.9 million base salary.
Second-year player Da'Norris Searcy began challenging Wilson for the starting job last season.
The Bills have a big question mark at free safety, with starter Jairus Byrd eligible to become an unrestricted free agent next month.
Veteran defensive lineman Spencer Johnson, defensive end Kyle Moore and linebackers Bryan Scott, Kirk Morrison and Shawne Merriman have also completed the final years of their contracts.
Buffalo's defense is prepared to undergo yet another transformation under Pettine, the unit's third coordinator in three years. Pettine is more accustomed to running a 3-4 alignment after the Bills reverted to a 4-3 system under former coordinator Dave Wannstedt last year.
The Bills struggled in making the transition last year, and despite the free-agent addition of defensive end Mario Williams, who was signed to a six-year, $100 million contract.
Buffalo (6-10) finished 31st in the NFL against the run, and 26th in allowing an average 27 points per game.