si ▁( J oe ▁M ante g na ), ▁senior ▁super vis ory ▁special ▁agent ▁( se asons ▁ 3 – 1 5 ) ▁ ▁Ros si ▁is ▁a ▁highly ▁experienced ▁profil er ▁who ▁once ▁worked ▁the ▁B AU ▁in ▁its ▁orig ins , ▁then ▁took ▁early ▁ret irement ▁in ▁ 1 9 9 7 ▁to ▁write ▁books ▁and ▁go ▁on ▁lecture ▁t ours ▁about ▁criminal ▁analysis , ▁until ▁volunte ering ▁to ▁return ▁shortly ▁after ▁SS A ▁Jason ▁G ide on ' s ▁departure ▁in ▁ 2 0 0 7 . ▁He ▁has ▁been ▁married ▁three ▁times ▁and ▁is ▁quite ▁wealth y ▁because ▁of ▁his ▁successful ▁writing ▁career . ▁In ▁the ▁episode ▁" From ▁Child hood ' s ▁H our " ▁( season ▁ 7 ), ▁David ▁re connect s ▁with ▁his ▁first ▁wife , ▁Carol yn ▁Baker , ▁who ▁has ▁shock ing ▁news ▁for ▁him . ▁It ▁is ▁revealed ▁that ▁she ▁came ▁to ▁him ▁because ▁she ▁was ▁diagn osed ▁with ▁A LS ▁( Lou ▁Ge hr ig ' s ▁disease ) ▁and ▁wants ▁David ▁to ▁assist ▁in ▁her ▁suic ide . ▁In ▁the ▁next ▁episode ▁(" E p ilog ue "), ▁Carol yn ▁dies ▁after ▁taking ▁a ▁drug ▁over d ose . ▁It ▁is ▁also ▁revealed ▁in ▁this ▁episode ▁that ▁David ▁had ▁a ▁son ▁who ▁died ▁at ▁birth . ▁In ▁the ▁season ▁ 8 ▁episode ▁" The ▁F allen ", ▁it ▁is ▁revealed ▁that ▁David ▁was ▁a ▁Marine ▁in ▁Vietnam . ▁The ▁season ▁ 7 ▁finale ▁(" H it ") ▁reve als