▁him ▁that ▁the ▁man ▁was ▁not ▁the ▁real ▁murder er . ▁Matth ä i ▁felt ▁that ▁there ▁was ▁a ▁serial ▁k iller ▁at ▁work , ▁with ▁the ▁girl ' s ▁murder ▁being ▁related ▁to ▁other ▁child ▁mur ders ▁that ▁had ▁occurred ▁in ▁the ▁area . ▁However , ▁he ▁was ▁alone ▁in ▁that ▁assess ment ▁and ▁the ▁police ▁closed ▁the ▁case . ▁ ▁Having ▁made ▁a ▁solemn ▁promise ▁to ▁the ▁parents ▁of ▁the ▁murder ed ▁girl ▁that ▁he ▁would ▁find ▁the ▁cul prit , ▁Matth ä i ▁abandoned ▁the ▁plans ▁he ▁had ▁made ▁for ▁his ▁life ▁in ▁ret irement ▁and ▁instead ▁continued ▁investig ating ▁the ▁case ▁as ▁a ▁private ▁citiz en . ▁He ▁was ▁war ned ▁by ▁a ▁psych iat rist ▁that ▁the ▁murder er ▁he ▁sought ▁likely ▁did ▁not ▁exist ▁and ▁thus ▁he ▁might ▁drive ▁himself ▁mad ▁with ▁his ▁ob session ▁in ▁finding ▁the ▁man . ▁Matth ä i , ▁however , ▁was ▁und eter red . ▁ ▁Through ▁sh rew d ▁detect ive ▁work , ▁and ▁driven ▁by ▁a ▁growing ▁and ▁near ▁man ia cal ▁ob session ▁with ▁the ▁case , ▁Matth ä i ▁was ▁able ▁to ▁construct ▁a ▁detailed ▁profile ▁of ▁the ▁likely ▁k iller , ▁down ▁to ▁the ▁very ▁road ▁the ▁murder er ▁would ▁probably ▁travel ▁to ▁and ▁from ▁his ▁evil ▁de eds . ▁Matth ä i ▁purchased ▁a ▁gas ▁station ▁along ▁the ▁route ▁and ▁then ▁h ired ▁a ▁house keeper ▁with ▁a ▁daughter ▁named ▁Ann em arie , ▁who ▁matched ▁the ▁profile ▁of ▁the ▁murder ed ▁girls . ▁With