He was smart to leave his cell phone in the car.
Shutting down here....nite all.
He was smart to escape. He was the key.
If he hadn't escaped, he'd probably be dead, and Speed Bump and Joker probably would have made it to Manhattan, and who knows how many Americans their remaining munitions might have killed?
Remember, before he escaped, all the cops had to go on was the fact that Officer Collier had been killed by unknown person(s). There was no vehicle description to be on the lookout for. Nobody had witnessed and reported the carjacking.
Later that evening, the FBI released the first usable resolution photos showing the perps' faces. The earlier videos didn't show their faces adequately — only people who knew them would have been alerted (e.g. Mrs Speed Bump, Katherine Russell Tsarnaeva). Her worried, questioning call to her husband was probably the catalyst that set them on the move. Too bad it resulted in Officer Collier's death.