PHOENIX - Security cameras inside a Circle K convenience store -- near 35th Avenue and Encanto Boulevard in Phoenix -- captured the moment a masked man with a knife walked into the store and threatened the clerk with the weapon in an attempted armed robbery.

“He takes that knife, starts yelling at the man and tries to get back behind the employee counter,” said Sgt. Jonathan Howard, a spokesperson for the Phoenix Police Department.

What the suspect may not have known was that an off-duty, armed and fully uniformed police officer was also in the store working as security.

"The officer and the suspect both stopped, confronted each other and had a brief verbal exchange,” Howard told 12 News.

If you're thinking, the suspect is about to get arrested by the officer, think again.

In the video you can see at the bottom of the screen someone approaches the man just before he taunts the camera with a smile and walks away.

The suspect remains on the loose and police are now hoping for help identifying him in order to make an arrest.

"The officer did not choose to make an immediate arrest and right now there have been people who've brought up concerns about that,” said Howard.

Why the officer let an armed robbery suspect leave the scene is now part of an internal investigation.

“If you're wearing a Phoenix police uniform and working in an off-duty capacity, the expectation would be that you provide the same level of service working in an on-duty or off-duty capacity,” Howard said.

Police also confirm the officer didn't radio anyone about the incident

They say she did call dispatch to generate a report number but the report wasn't turned in until days later.

"She did make an effort to stop the crime she did make an effort to report the crime, right now we're looking at her decision not to make more of an effort to make an immediate arrest,” said Howard.

The officer has been reassigned to desk duty pending the outcome of the internal investigation.

Police describe the suspect as a Hispanic man, 35 years old, 5-foot-5, 140 pounds with black hair, brown eyes and a mustache.

Police said he was wearing a flannel shirt, shorts, black shoes, black sunglasses, a gray baseball hat and a black bandana on his face.

If you have any information on the identity of the suspect or his whereabouts you’re asked to call Silent Witness at 480-WITNESS (948-6377).