Martin and Cook arrive as Brown leaves in free agency frenzy

The San Francisco 49ers have been busy in the first days of free agency, and have now brought in four players following a further addition on Friday.

Offensive lineman Jonathan Martin just missed the cut for my previous blog post, signing late on Tuesday in a trade from the Miami Dolphins.

San Francisco parted with an undisclosed draft pick to acquire Martin, whose short NFL career has been enveloped by controversy.

Martin has not played a down since late October, when he left the team as a result of harassment against him from team-mates Richie Incognito, Mike Pouncey and John Jerry, the extent of which was revealed in a report commissioned by the NFL.

The 24-year-old tackle will get a fresh start in the Bay Area, reuniting with 49ers' head coach Jim Harbaugh, who coached Martin during his collegiate career at Stanford.

Martin, who has played at both ends of the offensive line, is likely to operate as a 'swing tackle' and work as an extra lineman in the 49ers' heavy formation.

And Martin is looking forward to working with Harbaugh as he aims to get his NFL career back on track.

"I'm just looking forward to getting back to playing football," Martin said. "It's a blank slate for me. I'm looking forward to revitalizing my career."

"His (Harbaugh's) enthusiasm is infectious. You can see it at every level of the organization it rubs off on anybody. Being with an organization focused on winning is the best thing I can ask for.

"Hindsight is 20-20. My focus is 100 percent on the future and moving forward.

"I want to do whatever I can do contribute to this o-line. It's one of the best o-lines in football already. They have five great starters and I'm going to do whatever I can to help the team."

On the defensive ball the 49ers have not retained free-agent cornerback Tarell Brown, who has made the move across the bay to join the Oakland Raiders.

Brown has signed a reported one-year $3.5million deal, as per ESPN's Adam Schefter, to join the Raiders and will line up against the Niners when Oakland hosts San Francisco in 2014.

The 49ers have negated the loss of Brown somewhat by bringing in cornerback Chris Cook from the Minnesota Vikings.

Cook, who measures in at 6'2" and 200 pounds is a big, long-armed cornerback, but struggled in four seasons with the Vikings, failing to grab a single interception.

In a conference call with Bay Area reporters, Cook said the Niners see him as a "press guy", and - much like Martin - that he sees his move to San Francisco as a fresh start.

There is very little risk involved in the Cook deal, and the 49ers will hope that secondary coach Ed Donatell can help the former second-round pick quickly turn his career around.

The 49ers do not appear finished in free agency, instead it could yet be the case that they add further depth to their roster in the coming days.

New England Patriots' wide-receiver Julian Edelman and Seattle Seahawks' cornerback Walter Thurmond III - as per SB Nation - were both scheduled to visit with the 49ers on Friday, while Pittsburgh Steelers' receiver Emmanuel Sanders is set to do the same on Saturday.

Thurmond would not be the first player to cross the Seattle-San Francisco divide but, after playing a considerable role in the Seahawks' title success, it is a move that would not go down well among fans of the NFL champions.

The 26-year-old, who has also visited with the Jacksonville Jaguars, played in the Seahawks' nickel defense last season, and could easily fill the same role for the 49ers.

Edelman is coming off a season that saw him gain over 1000 yards receiving and score six touchdowns.

Both he and Sanders, who totalled 740 yards and six touchdowns in 2013, could provide the 49ers with options on offense and the return game, although it is the latter that may prove to be the cheaper and more realistic solution for Jim Harbaugh's men.

Meanwhile, 49ers' free-agent running back Anthony Dixon has tweeted that he is to join the Buffalo Bills following four seasons with San Francisco.