which was as follows -- may 4th, 2006 around 2 p.m., the gps headed out toward catalina island. the back side, where it seemed to putter around aimlessly in the middle of the night. then returned back to the dock 6:00 a.m. may 5th. that little device seemed to pinpoint the place and time of steven's murder. but how could detectives be sure the gps belonged to harvey and was on his boat? and then, what do you know. luck again. when harvey bought the gps, he took a friend. >> i was with him in the car when we picked it up. and it was such a cool gps. i've got one myself. >> that gps was a pivotal point in the investigation that really kind of sealed this whole case together. >> reporter: but though the gps evidence told detectives where harvey's boat was the day steven was killed, how could they be sure harvey and steven were together on the boat at precisely that time? >> electronic data is fascinating nowadays. very fascinating. our cell phones, we can also follow that signature. we were lucky again. >> reporter: lucky this time because of blackjack. blackjack cell tower, catali