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After nearly three weeks as a free agent, cornerback Brent Grimes opted to leave the Falcons for the Dolphins.

Why the Dolphins?

“I picked Miami because I think they are building something great here and I would love to be a part of it,” Grimes said Saturday, via the team’s official website. “They really showed a lot of interest in having me here. That played a major role in me deciding to come to Miami.”

Before Grimes can do much of anything for the Dolphins, he needs to get healthy again after tearing an Achilles tendon during the first game of the 2012 regular season.

“I am doing great,” Grimes said. “I am really encouraged by this rehab. I look it as a challenge and I respond well to challenges and I am 100 percent confident that I will be straight in no time. . . .

“I don’t have any restrictions right now. I am running and everything. It’s just building up your strength and everything. That’s part of the process, but I have plenty of time. With the offseason workouts and getting everything in shape, I will be great.”

Grimes will replace Sean Smith, who signed a three-year contract earlier this month in Kansas City. He’s the latest new arrival on a list that includes receiver Mike Wallace, linebacker Dannell Ellerbe, linebacker Philip Wheeler, receiver Brandon Gibson, tight end Dustin Keller, guard Lance Louis, and defensive tackle Vaughn Martin.