The Vikings signed Barr, the ninth overall pick, and Exum, a seventh-rounder, on Wednesday. They announced the deal for Crichton, a third-round pick, on Thursday.
Barr, a linebacker from UCLA, is expected to immediately upgrade a position group that struggled to make big plays last season. He had 23 1/2 sacks in two seasons for the Bruins after making the switch from running back.
Exum is a safety from Virginia Tech and Crichton is a pass-rushing end from Oregon State. He had 7 1/2 sacks for the Beavers last season.
The moves leave third-round running back Jerick McKinnon as the only player unsigned from the Vikings' 2014 class.
AP NFL website: www.pro32.ap.org and www.twitter.com/AP-NFL