Cason, a former University of Arizona standout, was a first-round draft pick by San Diego and never missed a game in his five seasons with the Chargers. Cason started all 16 games in 2012 with two interceptions, 71 tackles, one forced fumble and a team-high 12 passes defensed.
Earlier Friday, Arizona announced it had agreed to terms with Shaughnessy, who started all 16 games last season with Oakland. He had 3.5 sacks along with 42 tackles, 29 solos.
The Raiders selected Shaughnessy in the third round of the 2009 draft out of Wisconsin, where he was a teammate of Cardinals outside linebacker O'Brien Schofield.
Arizona has acquired eight free agents this week.