Williams was in training camp with the Redskins last year, but he broke his left pinkie and was released. He spent three seasons with the Tennessee Titans, catching 84 passes, but he hasn't played in an NFL game since 2007.
Hagans also spent last year's camp with the Redskins but was cut before the final preseason game.
Green has played in 49 games with five teams over six NFL seasons. Torain played two games in 2008 with the Denver Broncos under new Redskins coach Mike Shanahan.