NOTE: THIS ARTICLE HAS BEEN CORRECTED.

THEIR ADRENALINE pumps, their eyes dart back and forth and they inhale short, panicked breaths. With a gun in hand, they try to make a quick escape from the scene of their crime.

Suddenly, unexpectedly, they come face-to-face with a cop. They raise the gun and quickly pull the trigger.

A Philadelphia police officer is dead.

And in that split-second, they become cop-killers.

In the latest slaying of a Philadelphia cop, a massive hunt continues for Eric DeShawn Floyd, the only suspect still being sought in last weekend's slaying of Sgt. Stephen Liczbinski.

Experts say that most cop-killers have criminal records - as do alleged cop-killers Floyd and accomplices Levon Warner and Howard Cain - but that's not always the case.

What they share, however, is an impulsive, fatal decision made in the heat of the moment shortly after or in the midst of committing a crime.

Chad Lassiter, adjunct professor for the Graduate School of Social Policy and Practice at the University of Pennsylvania, is convinced that cop-killers can be easily detected.

Look for people with no hope, he said. "They're walking time bombs."

Philadelphia has endured three fatal cop shootings in two years. All but one of the shooters have long rap sheets.

Floyd, 33; Warner, 39, and Cain, 33, had a history of robbing people. They set out to rob the Bank of America branch inside the ShopRite on Aramingo Avenue Saturday morning, disguised as female Muslims, police allege.

They fled the bank and Liczbinski, responding to a radio call about the robbery, saw the suspects' van and followed it several blocks, to Almond and Schiller streets, in Port Richmond.

Liczbinski, a married father of three who would have turned 40 yesterday, was exiting his cruiser when Cain allegedly fired a Chinese-made SKS assault rifle at him from a short distance away and killed him.