so placentia p.d.rce the investigation to the cold case unit at the orange county d.a.'s office to a guy named larry montgomery. with more than 30 years working homicide, larry's put away a his share of bad guys, not usually by knocking on doors. instead, larry works by looking very closely at the evidence. he doesn't work fast. in fact, larry is meticulously slow. and that was just what this cold case needed. was there anything in the original investigation that struck you as something that you needed to re-examine? >> everything. >> reporter: everything that had led placentia police into that wall, trying to decide between two suspects. >> i mean, i'm concerned about this girl. okay, you know? and she's missing. >> reporter: marty, lynsie's older friend who kept their relationship a secret and lied about his name. and chris -- >> reporter: and so larry sat down and read through the entire case file. all the witness statements. all the interviews. he did that for two years. >> here we go down this roa