The announcement was made Tuesday by head coach Carl Franks.
Johnson, who has one season of eligibility remaining, has been granted a release to play football at Fordham.
"You never like situations when players must leave the program," Franks said. "We invested a great deal of time and effort in working with Shawn, but this outcome was inevitable and probably in the best interests of everyone involved.
"Shawn was our lone first team all-conference selection, and his individual success certainly was in part due to the efforts of those players around him. Football is a team sport, and in order to be successful, all 11 players must execute within the system."
Johnson earned first-team All-ACC honors in 2002, recording 73 total tackles, including 19.5 tackles for loss and 12 sacks.
Johnson is one of five lettermen not returning for the Blue Devils in 2003, joining linebacker Kurt Miller, defensive end Chad Rice, safety Anthony Roberts and linebacker Jamyon Small.
Duke, which begins spring practice March 17, opens the 2003 season at Virginia on Aug. 30.
Copyright 2023 by Capitol Broadcasting Company. All rights reserved. This material may not be published, broadcast, rewritten or redistributed.
