An expert revealed to the Daily Mail how to handle an active shooter if they storm into your building.

Marty Adcock, who transitioned to a law enforcement career following his service in the Marines, served as the program manager for the Advanced Law Enforcement Rapid Response Training initiative based at Texas State University.

He offered courses to teach cops and other officials how to prepare regular citizens for unexpected gun attacks.

ALERRT was created in 2002 and in 2013 was named the National Standard in Active Shooter Response Training by the FBI.

No one expects it to happen to them – a deadly mass shooting interrupting their ordinary routine.

But tragically, it does, as the world was reminded this week when a gunman stormed the Blackstone building reportedly hunting NFL staff.

The world got a stark reminder this week when an attacker entered the Blackstone building with the reported intent of targeting NFL personnel. Pictured: Blackstone employees securing a doorway.

Active shooters have targeted unsuspecting individuals in a variety of locations, including offices, salons, schools, and nightclubs. According to experts, key elements for surviving such events are being prepared and staying aware of one’s surroundings.

Law enforcement officials across the US train civilians how to react in active shooter situations, which occur about once every three weeks, according to the FBI.

Speaking in 2017 after the horrific Las Vegas massacre, instructor Louis Rapoli – who spent 25 years with the NYPD – said: ‘We’re trying to program that hard drive in the brain, so when something does happen, people will have a response planned and have something to do should a critical incident happen.

While he was assigned to the School Counter-terrorism unit, he conducted threat assessments and investigations and trained law enforcement and civilians in active shooter response.

‘Avoid, Deny, Defend’ may sound like common sense, but in a panic, people often aren’t thinking clearly; it helps, instructors insist, to have the strategy firmly embedded in their memories beforehand.

First, civilians stuck in an active shooter situation should try to get as far away from the attacker as possible: that’s the ‘avoid’ instruction.

If that’s not an option, however, they need to ‘deny’ access to their location, ideally locking a door, creating a barricade and turning off the lights.

Even a belt can be used to jam a doorway, for example. Most active shooters want to kill as many people as possible in the shortest space of time, Mr Rapoli said.

‘People that are in locked locations don’t tend to get killed in active shooter events,’ he said, describing such attackers as looking for the ‘path of least resistance … they’re like water.’

Finally, if there’s no way to avoid or deny the shooter, potential victims need to defend themselves – using whatever means necessary and looking around for anything that could be used as a weapon.

Retired Sgt Rapoli used an example of how most police officers, when in a restaurant, will sit near the kitchen; not only does that offer access to a secondary exit, but the kitchen also offers ‘weapons’ in the form of knives, pots, pans and other items.

He teaches the CRASE course around the country, which focuses heavily on one thing: action.

ALERRT never advises playing dead as a strategy and uses the 2007 Virginia Tech shooting as a case study to show that rooms that played dead had higher fatalities.

Heavily-armed officers were seen rushing into the skyscraper in New York City following the Blackstone building shooting

But tragedies such as the Las Vegas massacre offer their own unique challenges – particularly if victims can’t locate the origin of the gunfire.

The ‘Avoid, Deny, Defend’ strategy still applies, Mr Adcock said, but it’s all about ‘finding yourself in a position where you can… look for something that would provide a hard cover ballistic protection to deny them access to you.’

Referring to the Las Vegas shooting, he said: ‘Where they were at, you could see quite a few of the barricades are just lattice-type bar steelwork that really did not provide a solid barrier.

‘So avoiding, trying to move out of the affected area, getting out of range of the affected area is going to be the biggest thing.

‘So yes, Avoid, Deny Defend still applies, but how do you defend yourself against something like that?’ he said of the Vegas gunman’s high location.

He added: ‘Being that it’s a very flat area out there and the overview of the concert venue from Mandalay Bay is unobstructed, there’s really nothing … so moving further away, outside the venue, putting vehicles or other barriers between you and the affected area, is going to be your only option on that one.’

If a gunman opens fire from the ground at such a crowded event, he said: ‘If you’re in very close proximity – we’re talking, you know, arm’s distance, even small room distance – or avoiding is not going to be an option, you may have to go, ‘Avoiding or denying is not an option.’

‘You may have to go immediately to the defend mode and try to somewhat take the fight to the attacker, get your hands on the weapon.

‘If it’s a firearm, try to get the weapon pointed to a direction where it can’t cause you or anyone else harm.’ 

If one person begins to act in self-defense, he said, other potential victims also often step up in an effort overpower the attacker.

‘Once you have started the defense process, normally you’re going to see that other people will pile on and help you out – so it’s an immediate trying to enlist others to save themselves,’ he said.

Civilians also need to learn what gunshots sound like, instructors said, even if that just means playing an audio file to groups being taught by law enforcement officials.

Instructors urge vigilance and warn against the complacency that comes with routine. ‘Don’t think that nothing can happen,’ Mr Rapoli said.

‘I think people need to go into this with an open mind and realize that anything can happen … to be prepared, rather than to not be prepared.

‘If you’re not prepared, you’re going to default to your training, which is nothing – and then bad things are going to happen.

‘So I would say everybody should open their minds and say, ‘Hey, this can happen’ – and be prepared.’