Butler, 28, spent six years with the St. Louis Rams, but missed the
2005 season with a knee injury and played sparingly after returning last year.
Butler, a fifth-round draft pick out of Kansas State in 2001,
played in 63 games with 31 starts for the Rams. His best season was
2004, when he had five interceptions and 79 tackles.
The Rams did attempt to trade Butler during this year's draft, but found no serious suitors at the time, in part because of Butler's contract. His deal with the Rams had three years remaining, at base salaries of $2 million (2007), $2.5 million (2008) and $3 million (2009).
Butler's career began to spiral, however, when he suffered a season-ending knee injury in the team's 2005 training camp. After Butler rehabilitated the surgically repaired knee, he sustained a serious hamstring injury last summer in camp.
Information from The Associated Press and ESPN.com senior writer Len Pasquarelli was used in this report.