Warren spent the 2010 season with New England after also playing for Oakland, Denver and Cleveland in a 10-year NFL career. He finished with 36 tackles and 3 1/2 sacks in 16 games, including 10 starts, last year.
The veteran was selected by Cleveland with the third overall pick of the 2001 NFL Draft after a stellar career at Florida. He has compiled 35 1/2 sacks and 303 tackles with seven forced fumbles and four fumble recoveries in 151 games.
Butler played two seasons with the Patriots after being selected by the club in the second round of the 2009 draft out of Connecticut. He appeared in 29 games, making eight starts, and registered 61 tackles with three interceptions during his two seasons with the team.
The Patriots also signed tight end Dan Gronkowski and were awarded linebacker A.J. Edds off waivers from the Miami Dolphins.
Gronkowski has played in 14 games over two seasons with Detroit and Denver. He started four of the 12 games he played for the Broncos last year and caught eight passes for 65 yards.
Edds was selected by the Dolphins in the fourth round of the 2010 draft. The Iowa product spent his rookie season on injured reserve with a knee injury.