, ▁he ▁finds ▁Re ed ' s ▁back pack ▁on ▁the ▁floor ▁of ▁his ▁a partment ▁hall way , ▁and ▁his ▁keys ▁still ▁in ▁the ▁lock . ▁Back ▁at ▁the ▁lab , ▁he ▁real izes ▁that ▁Re ed ▁has ▁been ▁kid n apped ▁by ▁his ▁source — the ▁C abb ie ▁K iller ▁himself . ▁Mac ▁is ▁extremely ▁wor ried ▁for ▁his ▁steps on ' s ▁life . ▁Through ▁posts ▁on ▁Re ed ' s ▁blog , ▁the ▁team ▁is ▁able ▁to ▁locate ▁the ▁C abb ie ▁K iller ▁and ▁the ▁now ▁injured ▁Re ed . ▁Mac ▁stays ▁with ▁Re ed ▁at ▁the ▁hospital , ▁and ▁after ▁catch ing ▁the ▁C abb ie ▁K iller , ▁takes ▁him ▁home . ▁ ▁In ▁the ▁line ▁of ▁duty ▁Mac ' s ▁bad ge ▁number ▁is ▁ 8 4 3 3 . ▁An ▁NY PD ▁Medal ▁for ▁Val or ▁certificate ▁is ▁seen ▁fr amed ▁and ▁mounted ▁in ▁his ▁office ▁in ▁the ▁season ▁ 6 ▁episode ▁" Rest ▁in ▁Peace , ▁Marina ▁Gar ito ". ▁ ▁Mac ▁keeps ▁a ▁p ile ▁of ▁un sol ved ▁cases ▁on ▁the ▁corner ▁of ▁his ▁des k . ▁Rap ist / m ur der er ▁DJ ▁Pr att ' s ▁file ▁remained ▁there ▁for ▁some ▁time , ▁until ▁the ▁CS Is ▁closed ▁it ▁with ▁the ▁post hum ous ▁assistance ▁of ▁former ▁colle ague ▁A iden ▁Burn . ▁Mac ▁says ▁the ▁p ile ▁used ▁to ▁be ▁bigger , ▁which ▁helps ▁validate ▁his ▁feelings ▁about ▁being ▁a ▁C SI . ▁He ▁usually ▁sacrific