On Day 1, Bills Seek Williams and the Dolphins Trade Marshall Miami traded Brandon Marshall to Chicago. The most prominent free agent, Peyton Manning, remained unsigned Tuesday, but the impact of the passing game shaped the first day of N.F.L. free agency. The early blockbuster moves centered on teams vacuuming a deep class of wide receivers and the aggressive push by the Buffalo Bills to lure the top available pass rusher. Linebacker and defensive end Mario Williams, a former first-round pick of the Houston Texans who is considered the best defensive player available among the 532 free agents, arrived in Buffalo less than two hours after free agency began at 4 p.m. Eastern, with the Bills expected to try to keep him from leaving without agreeing to a contract. Moments after free agency began, the Chicago Bears made a surprising move, acquiring the Pro Bowl receiver Brandon Marshall in a trade with Miami. The Dolphins gave up two second-round draft picks to acquire Marshall from Denver two years ago, but received two third-rounders from the Bears. The move leaves the Dolphins and their new coach, Joe Philbin, with no No. 1 receiver. The Dolphins are in the market for a new starting quarterback - they have met with Manning - but it also removes the headache of Marshall's complaints about quarterbacks while Philbin incorporates a new system. The trade reunites Marshall with Jay Cutler. Marshall and Cutler worked well together in Denver from 2006 to 2008, and they are joined in Chicago by Jeremy Bates, who worked in Denver and is now the Bears" quarterbacks coach. Marshall caught 81 passes for 1,214 yards last season, and he could finally give the Bears the receiving threat they have lacked. Chicago has not had a 1,000-yard receiver since Marty Booker in 2002. The Washington Redskins, who moved into the second overall draft spot to take Baylor quarterback Robert Griffin III, were trying to sign almost everyone else in what has become their annual - and all-too-often fruitless - cannonball into free agency. They overhauled their receiving corps even though the N.F.L. has docked them $36 million in cap space over the next two years because of what the league said were improperly structured contracts during the 2010 uncapped season. First, they reeled in the former Indianapolis receiver Pierre Garcon, who will provide a speedy downfield - though drop-prone - threat. Fox Sports reported that the five-year contract includes a staggering $21.5 million in guaranteed money, which puts him behind the $24 million in guarantees Santonio Holmes got from the Jets, remarkable for a player who has never had a 1,000-yard season. The Redskins also negotiated with the former San Francisco receiver Josh Morgan and the former Broncos receiver Eddie Royal. While the Redskins were remaking their offense, New Orleans was making sure its powerhouse unit stayed largely intact, signing receiver Marques Colston to a five-year deal before free agency began. The most intriguing signing, though, may have been the one that happened nearly 24 hours before free agency began. Randy Moss, who did not play last season, signed a one-year contract with the San Francisco 49ers late Monday night after a workout in which he caught passes from Coach Jim Harbaugh. In 2010, an unhappy Moss was with three teams and caught only 28 passes. But Moss has apparently retained his speed, and if he remains healthy and committed to playing hard, the low-risk contract - there was no guaranteed money - provides the 49ers and the likely starting quarterback Alex Smith with the vertical threat their passing game lacked in 2011, when they lost the N.F.C. championship game to the Giants. THOMAS STAYS WITH JETS The Jets re-signed the outside linebacker Bryan Thomas for another year. The team selected Thomas in the first round of the 2002 draft. Thomas, 32, missed the final 12 games last season after tearing his Achilles" tendon on Oct. 2. No one from a group including Josh Mauga, Garrett McIntyre and Jamaal Westerman distinguished himself as a full-time replacement. Retaining Thomas, 32, should not preclude the Jets from pursuing additional help at the position, and they could make a play for Jarret Johnson, a longtime favorite of Coach Rex Ryan's from Baltimore.