▁the ▁ 1 9 9 0 s ▁currently ▁serving ▁two ▁life ▁sentences , ▁did ▁not ▁act ▁alone ▁and ▁that ▁his ▁accomp lice ▁had ▁begun ▁killing ▁again . ▁R ather ▁than ▁leave ▁in ▁the ▁middle ▁of ▁a ▁case , ▁Gr iss om ▁stayed ▁on ▁to ▁help ▁solve ▁it , ▁and ▁ultimately ▁proved ▁instrument al ▁in ▁saving ▁the ▁life ▁of ▁a ▁woman ▁who ▁would ▁have ▁been ▁the ▁k iller ' s ▁latest ▁victim . ▁The ▁case ▁closed , ▁Gr iss om , ▁having ▁already ▁had ▁a ▁series ▁of ▁one - on - one ▁fare well s ▁with ▁his ▁co - work ers , ▁sil ently ▁left ▁the ▁crime ▁lab ▁and ▁depart ed ▁for ▁Costa ▁Rica ▁for ▁a ▁re union ▁with ▁f ian c ée ▁S ara ▁Sid le , ▁an ▁all usion ▁perhaps ▁to ▁his ▁comments ▁in ▁a ▁season ▁one ▁episode ▁that ▁when ▁he ▁left , ▁people ▁would ▁not ▁throw ▁a ▁party ▁for ▁him ▁because ▁he ▁was ▁not ▁the ▁sort ▁of ▁person ▁who ▁people ▁would ▁get ▁deeply ▁involved ▁with . ▁He ▁also ▁says ▁to ▁W arr ick ▁in ▁season ▁two ▁(" E ll ie ") ▁that ▁when ▁he ▁left ▁there ▁would ▁not ▁be ▁a ▁c ake ▁in ▁the ▁break ▁room — he ▁would ▁just ▁pick ▁up ▁and ▁leave . ▁ ▁After ▁C SI ▁ ▁After ▁re unit ing ▁with ▁S ara ▁Sid le , ▁Gr iss om ▁pres umably ▁remains ▁in ▁Costa ▁Rica ▁for ▁a ▁short ▁time , ▁before ▁guest - lect uring ▁at ▁the ▁Sor bon ne , ▁as ▁noted ▁in ▁the ▁t enth