After Meng was ordered to drive to Watertown, he drove into Cambridge, pulling into a Shell station on Memorial Drive. Dzhokhar Tsarnaev can be seen in surveillance video at the station walking into the store and browsing the aisle for snacks. While Dzhokhar was in the store, Meng took the opportunity to dart out of the door, run across the street to a Mobil gas station, and asked the clerk there to call the police.
Meng hid inside the gas station while he called 911. Within seconds, police arrived.
Above is footage of Meng's escape.