this to my family. he did this to crystie. he did this to momo. he did this to my mom and michelle, to javonte, to all of us, and -- >> and he got away with it. >> and he got away with it. >> reporter: even detective robbie williams saw derek one day at the airport. >> my wife and i were on our way to a vacation. and i look up and i see derek walk right past us. >> reporter: williams had never forgotten crystal taylor. he'd had taken her case file with him as he moved up the promotional ladder from detective to lieutenant. he'd always shared the family's suspicions that derek was somehow behind crystal's murder. but he also knew he didn't have enough evidence to arrest him. >> i whispered to my wife, "that's the guy. that's the guy who had crystal taylor killed." >> that's got to be like a knife in you. i mean, if that's what you think, if you think that's the guy who had crystal taylor killed, well here he is, out free, breathing the same air you are. maybe going on vacation just like you are. having a great time.