Murphy, whose acquisition was announced Sunday, was selected by the Rams out of South Florida in the third round of the 2010 draft. He played in 14 games as a rookie before missing all of 2011 with a broken ankle.
In his rookie season, Murphy was credited with 30 total tackles and an interception, along with seven special teams tackles and a fumble recovery. He sought to come back this season with the Rams, who cut him at the end of the preseason.
Mack is a fifth-year cornerback signed by New Orleans during the past off-season. He played the past four seasons with Tampa Bay.