James A. Gagliano is a CNN law enforcement analyst and a retired FBI supervisory special agent. He also serves as an adjunct assistant professor at St. John's University in Queens, New York. Follow him on Twitter: @JamesAGagliano . The views expressed in this commentary are his own.

(CNN) The stunning news that surfaced a week after the mass shooting at Marjory Stoneman Douglas High School in Parkland, Florida, was hard to digest. An armed Broward County Sheriff's Office (BSO) deputy, Scot Peterson, assigned as a school resource officer, was on duty on that February afternoon. And yet he remained outside of the freshman building during the slaughter.

Peterson's lawyer claimed the way he acted was "appropriate under the circumstances," and that he did not run into the school because he thought the gunfire was coming from outside. He further added that "allegations that Mr. Peterson was a coward and that his performance, under the circumstances, failed to meet the standards of police officers are patently untrue."

Nonetheless, Peterson has since resigned and an investigation has been opened.

It's important to remember that after the 1999 Columbine shooting, there were new protocols established to address an active school shooter. A review of the law enforcement response at Columbine concluded that arriving officers elected not to enter the school buildings until a SWAT team arrived and made entry some 47 minutes after the first shots were fired.

In the business of saving lives, minutes -- and even seconds -- count. Awaiting the arrival and assembly of a SWAT team is therefore no longer the preferred practice. Instead, whoever is on scene is supposed to confront the shooter immediately, with the understanding that backup will be on the way. Peterson's failure to follow the immediate interdiction protocol shows that the lessons of Columbine have not yet been fully implemented and embraced.

Now I know not every member of law enforcement is a hero. And just like in every profession, some are better suited for the "business" than others. But sound training also conditions officers to control their fears and act heroically.

Tactics learned in law enforcement academies and in-service training contribute to this response conditioning. And in the almost 19 years since the Columbine shooting, law enforcement has reflected on the lessons learned from that massacre and adopted tactics to counter an evolving threat.

What was so unique about Columbine was that it was wholly unexpected and involved attackers in a bucolic suburban setting -- like Parkland.

And the police response was based on law enforcement's contextual understanding of hostage situations. In other words, law enforcement tactics in 1999 were still hopelessly rooted in the 1975 bank standoff tactics in Sidney Lumet's "Dog Day Afternoon." Responding police agencies at Columbine assembled in staging areas and formed a standard police perimeter.

Thinking at the time was centered on the theory of "contain and negotiate." What made Columbine unique in law enforcement annals was that the depraved killers were simply intent on racking up a large body count, with no real intention of surviving the attack.

Therefore, containment became an archaic approach. And waiting for a SWAT team to arrive and interdict a barricaded subject became an outdated construct.

Training in the early 2000s focused on the immediate coalescing of disparate arriving law enforcement elements into tactical formations that immediately moved toward the epicenter of danger. Local departments and state agencies began to train closely with their federal counterparts. And the new tactics became universally adopted.

The FBI's Hostage Rescue Team, located within the US Marine Corps base at Quantico, Virginia, has hosted active shooter training for units like the New York State Police's Special Operations Response Team. And FBI SWAT teams frequently host local police departments to share "best practices" and to ensure seamless coordination -- known as interoperability -- when responding officers from different departments converge on a scene.

In March 2014, the Police Executive Research Forum drafted another treatise in their "Critical Issues in Policing" series: "The Police Response to Active Shooter Incidents." Beyond the obvious acknowledgment that Columbine was the catalyst for tactical rethinking, it focused on an Associated Press accounting that highlighted the post-Columbine tactics shift:

"A deadly shooting at an Indiana grocery store could have been much worse if not for the quick actions of two police officers who relied on training that has become commonplace since the 1999 Columbine shootings. Cody Skipper and Jason Tripp arrived at the Elkhart store within three minutes and needed less than 60 seconds to fatally shoot a gunman who had killed two people and was threatening a third."

Responding Officers Skipper and Tripp skipped the first procedural step in the outdated "contain and negotiate" protocol -- establish a perimeter -- and moved immediately to confront the gunman. They didn't await arrival of a tactical team. While their actions assuredly presented more risk of danger to themselves, it undoubtedly saved lives.

So now that local reporting from the Miami-Herald charges that a BSO captain who arrived to take charge of the scene in Parkland issued a command directive to "form a perimeter," it may be indicative of department protocols that were not updated after Columbine.

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Sheriff Scott Israel, who actually hired the on-scene commander, Captain Jan Jordan, refutes that notion. He has stated he concurs with the national police consensus that places a priority on immediately confronting a shooter, rather than securing a scene. Israel also maintains that his department's sworn members are trained in these accepted practices.

But the BSO dispatch log obtained by the Miami-Herald indicates that is not what occurred. And that's unconscionable and may have led to the loss of more student and teacher lives.

Let's hope that the deep-dive investigation by the Florida Department of Law Enforcement into the factors that contributed to this tragedy provides us some answers.

Correction: This piece initially misidentified Sheriff Scott Israel as Steve Israel.