and they had over 90 minutes to spend with each other, and they were talking about ordinary things, what kind of phone do you have, do you have a cd player in the car. there was this kind of a relationship forming, which in -- eventually aided danny. >> reporter: but at one point danny's phone buzzed with two texts, then rang twice. >> danny answers it. tamerlan says, don't say a word in chinese, if you do, i'll kill you. so his friend is speaking chinese over the phone but danny answers in english. i'm going to sleep elsewhere tonight. and when he finally hung up, tamerlan said, good boy. you did it well. >> reporter: professor fox said the brief window for escape came at this shell station. cash only at the time so dzhokhar tsarnaev went in to pay cash for the gas. at that point tamerlan tsarnaev was briefly fumbling around with his personal gps system.