Street smarts, judgment, discretion.
Other than relying on those skills taught at the police academy and honed through experience, off-duty and retired law enforcement officers appear to have few rules to follow when confronting a crime out of uniform, like the apparent friendly fire that left a federal agent dead on New Year's Eve.
And when different police agencies are involved, with unfamiliar officers coming face to face and making snap decisions about life and death, the peril is greater, according to a 2010 New York state study of police-on-police shootings that called for uniform protocols across agencies.
The task force created in 2010 by then-Gov. David Paterson found "enormous variation" in how thoroughly departments across the country train for encounters between police officers in and out of uniform _ "if they train at all."
"The multiplicity of agencies is a source of many problems in policing, but it raises particular problems when officers from one agency confront an officer out of uniform from another agency, mistaking the confronted officer for a criminal," the report said.
John Capano, a 51-year-old off-duty agent for the federal bureau of Alcohol, Tobacco, Firearms and Explosives, was shot Saturday in Seaford while struggling with 43-year-old suspect James McGoey during a robbery for prescription painkillers and cash at a small family pharmacy. Capano, an explosives expert who served in Iraq and Afghanistan, was a customer and followed the suspect outside.
During Saturday's holdup, someone ran into a nearby deli and shouted that the drugstore was being robbed. A retired Nassau County police lieutenant and an off-duty NYPD officer who were in the deli ran to the pharmacy. Shots were fired, and Capano and McGoey were killed.
On Tuesday, a law enforcement official speaking on the condition of anonymity told The Associated Press the retired county officer likely shot Capano. Nassau County police have not commented on details, citing the ongoing investigation.
The task force that looked at protocols for out-of-uniform or retired officers included calls for improved communication and training, as well as creating across-the-board protocols for different agencies.
Since the report came out, training of police recruits on encounters with off-duty and plainclothes officers was doubled to four hours, said Janine Kava, a spokeswoman for the state Division of Criminal Justice Services. And thousands of officers statewide have taken courses for existing officers on police-on-police encounters, she said.
The agency also issued recommendations to law enforcement agencies in March 2011, offering guidance for developing policies on confrontations between uniformed officers and plainclothes or off-duty officers, agency spokeswoman Jessica Scaperoti said Wednesday.
Recommendations included requiring officers to carry photo IDs at all times and requiring them to be aware of their agency's policies regarding off-duty conduct, firearms possession and arrests. Also, off-duty officers should carefully consider whether intervention is necessary, including whether the health and safety of innocent people are involved.
They were only recommendations, not mandatory, and they do not appear to address retired officers except to note that "qualified retired law enforcement officers are authorized to carry a handgun throughout the United States."
Capano, a 23-year member of the federal firearms bureau who taught U.S. military members and local forces in Afghanistan and Iraq how to investigate explosions, likely wouldn't have been subject to the recommendations of the state agency.
Capano would have never backed off, an ATF supervisor said Wednesday.
"As law enforcement officers, we go to crimes; we don't run away from them. And that's exactly what he did. In his mind I'm sure he had no choice," said Eric Immesberger, the agent in charge of the ATF's Long Island office.
It wasn't clear whether Nassau County police distributed the recommendations to officers, current or retired. But Jon Shane, a retired Newark, N.J., police captain who is now a professor at John Jay College of Criminal Justice, said officers must rely on their instincts and experience.
"Presumably these are officers who have been trained throughout their careers on how to use a weapon properly," he said.
When officers retire, they must apply for pistol permits, as any citizen does, Shane said. On Long Island, which has been a bedroom community for New York City police officers since the 1950s, more than 17,000 pistol permits of the 66,000 issued are in the hands of retired officers.
The task force noted that although rare _ police-on-police shootings have averaged one a year in the United States for the past three decades _ many involve instances of white officers shooting blacks out of uniform. In the New Year's Eve case, both victims were white.
It was the second deadly holdup in a pharmacy on Long Island in 2011. In June, a gunman opened fire in a drugstore about 30 miles east in Medford, killing two employees and two customers before fleeing with a backpack filled with painkillers.
The shooting also appears to be the second friendly fire incident in Nassau County in the last year. A Nassau police officer in plainclothes was shot to death in March by a transit authority officer in Massapequa Park.
James Carver, president of the Nassau County Patrolman's Benevolent Association, noted significant differences in the two cases.
In March, uniformed officers were already at a domestic disturbance and had secured the situation when someone in the crowd of bystanders _ possibly a retired police officer _ saw what turned out to be an armed Nassau County officer in street clothes approaching the scene and yelled "Gun!"
A transit authority officer who was patrolling a nearby train station opened fire, killing the Nassau officer instantly. Lt. Kevin Smith, a Nassau police spokesman, said no public report was issued after the shooting and training issues were handled administratively.
In Saturday's case, no uniformed officers had arrived by the time Capano or the off-duty and retired officers became involved, Carver said. The ATF agent may have been mistaken for a robbery suspect.
"Every situation should be handled differently," Carver said. "But in general, no member of the general public, including off-duty or retired officers, should get involved if they see uniformed officers on the scene. Never interject yourself into what an active duty police officer is doing."
Neither the retired Nassau lieutenant nor the off-duty NYPD officer has commented publicly. A telephone call to the NYPD officer's home was not returned, and a woman answering the telephone at the deli where the retired lieutenant works said no one would comment.
Capano's family placed blame for the shooting on the robbery suspect. "We only blame one person for the whole thing, and that was the criminal," Tony Guerriero, Capano's brother-in-law, told Newsday. The two officers at the scene "were all there to do their job and it just played out the way it played out."
Associated Press writers Colleen Long and Verena Dobnik and AP researcher Rhonda Shafner in New York City contributed to this report.