It's not clear why Stephen Morgan didn't flee in the car he had parked outside the campus bookstore where he apparently shot Justin-Jinich. The working theory is that it may have been hemmed in by emergency vehicles.
Anyway, he was actually interviewed by a cop as a potential witness to the crime outside the campus bookstore where Justin-Jinish was shot; cops realized he was the shooter and launched a manhunt only after his name was mentioned by Justin-Jinich's family, and police realized they had spoken with him at the scene.
It's not clear that Morgan actually dated his victim, as earlier news reports indicated; instead he attended a summer "Sexual Diversity in Society" class with her at NYU before sending 38 harassing email messages and inundating her with phone calls. The two both come from Colorado so there's an outside chance they knew each other there.
The victim reported the harassment to police but declined to pursue it.
It's not yet clear how Morgan was caught. Officers are no doubt smarting over having Morgan him slip through their fingers once. But their fast response at least helped deter or block the suspect from the "Jewish Columbine" he planned in one of his journals. And that's one of the few positives in this tragedy.