Crowell, who missed all of 2008 because of a knee injury, was a third-round draft pick of the Buffalo Bills in 2003. Two years ago, he had the best season of his career, finishing 2007 with a team-leading 140 tackles, two sacks, one interception, one fumble recovery and one forced fumble.

The 27-year-old is joining a defense that's being overhauled after the release last month of starting linebackers Derrick Brooks and Cato June. He has started 41 of 65 career games and is expected to compete with Quincy Black and Adam Hayward for playing time at strongside linebacker.

The Bills agreed to a deal with Pat Thomas, who will take over for Crowell, a source told FOXSports.com. Thomas, a five-year NFL veteran, started a career-high nine games last season in Kansas City.