It’s taught to police across the country.
Officers use it to explain why they shot at someone.
Prosecutors, including in Utah, point to it when deciding if a police shooting was legal.
It’s called the “21-foot rule,” and it means that someone with a knife running toward police, could cover about 21 feet before officers unholster their gun and fire.
But this standard training technique, which got its start in Salt Lake City, is now controversial. It’s been called outdated, simplistic, even dangerous. It’s not based on science or the law. And some national policing leaders argue it shouldn’t be taught to cadets anymore.
Yet, new police officers still hear about it.
The 21-foot-rule has been cited directly by lawyers or police to justify shootings in five cases in Utah over the past 16 years, according to a Salt Lake Tribune database, expanded with the help of the PBS series FRONTLINE. In two others, tenets of the rule were referenced — such as specifying someone’s distance was within 21 feet — though it wasn’t outright mentioned by name.
That’s nearly 20% of the 37 cases during that time frame when someone had a knife when a Utah officer fired.
State officials who teach new officers say it’s not part of the official curriculum, though it is mentioned in training sessions.
Even with its prominence in policing culture, the Salt Lake City lawman behind it all said it was never meant to be a rigid rule.
‘How close is too close?’
It all started in 1982. Dennis Tueller was a sergeant then and was out on the shooting range with officers, practicing drawing and firing their weapons.
A new officer posed a question: When would he be justified in shooting someone coming at him with a knife?
“Essentially, they were asking how close is too close?” Tueller said in a 2018 YouTube video copyrighted by the Utah Attorney General’s Office. “I realized that I didn’t have a good answer for that.”
So Tueller assigned one officer to play the role of the aggressor. Another was the officer about to be attacked. The attacker would run toward the officer, and they would time how long it would take to reach him.
They did it over and over, with various role players. Men and women. Some smaller, others with larger builds.
“It was pretty consistent,” Tueller said. “And that was sobering. Because we thought we were doing pretty well being able to draw and shoot and engage a target at 7 yards in 1½ to 2 seconds. We came to realize that if all you do is stand there and wait for the attacker to come, and you draw and shoot, they can be on top of you before your bullet can take effect.”
Tueller published an article in SWAT magazine detailing his findings.
“Let’s consider what might be called the ‘Danger Zone’ if you are confronted by an adversary armed with an edged or blunt weapon,” he wrote. “At what distance does this adversary enter your Danger Zone and become a lethal threat to you?”
It was, he said, 21 feet.
The article never proposed a hard-and-fast rule, but it stuck.
Tueller, who declined an interview request, has also repeatedly said through the years that he never intended his experiment to be incorporated into police training and used in courtrooms to justify shootings.
“I have heard trainers use that bastardized term, ‘21-foot rule,’ to actually say that, well if you shoot someone further than 21 feet away, you could be charged with homicide,” Tueller said in the YouTube video. “Or someone inside of 21 feet, you’re justified in shooting.”
Should the 21-foot rule be taught?
Whether Tueller intended it to, the concept that’s known as the 21-foot rule or the “Tueller Drill” has taken a strong hold in American policing.
“I would argue that you couldn’t find a police officer anywhere in the United States that isn’t aware of the 21-foot rule,” said Randy Shrewsberry, executive director of The Institute for Criminal Justice Training Reform. “It’s not only a part of regular training but something we remind officers of over and over throughout their career.”
Shrewsberry and other advocates for police training reform have argued that the rule is too simplistic to be effective for today’s officers.
“It has no scientific basis at all,” Shrewsberry told a FRONTLINE reporter. “It was never published in any scientific journal. … The main fault with the 21-foot rule is that it provides no nuance. That 21 feet is assuming the ground is flat. It is assuming the speed of the would-be attacker. It is assuming whether or not the officer has his gun holstered.”
And it is possible that 21 feet isn’t enough.
A group of researchers did a scientific examination of the 21-foot rule that was published in 2020 in the academic journal Police Practice and Research. The researchers — William Sandel, M. Hunter Martaindale and J. Pete Blair — wrote that, after a series of tests in a laboratory setting, police need more space, and that “the term ‘safe distance’ has allowed the 21-foot rule to become a standard in the field, but it places officers in danger.”
“This is especially true when considering that officers tend to have a high rate of missing the target and that one shot rarely stops a suspect’s forward movement,” they wrote. “It is also important to note that this study took place in a laboratory setting, which gave the officers a best-case scenario and the greatest chance of success.”
Chuck Wexler, executive director of the national nonprofit Police Executive Research Forum, helps advise police departments on best practices. He said his organization started recommending to departments in 2016 that they eliminate the 21-foot rule from their training. He said he got some pushback at first — “Old habits die hard,” he said — but more agencies have gotten on board in recent years.
“It’s a simple, simplistic way of looking at a more complicated issue,” he said. “And it has unbelievably tragic consequences.”
Wexler said police officers should instead be taught to slow things down and create distance and try talking to an armed person to de-escalate an encounter before it becomes a confrontation. An officer should try to find cover, he said, instead of following an arbitrary rule that says they can shoot if anyone is within a certain distance with a knife.
“The answer to this is really thinking about tactics,” he told The Tribune, “and thinking about what you have to do to be able to successfully keep the officers safe and the subject they’re dealing with safe.”
Now a guideline, not a policy
Even though the 21-foot rule isn’t officially in policy manuals, it’s still being taught to Utah’s new officers.
Reporters with FRONTLINE and The Tribune heard training officers teach it during scenario-based exercises at the state’s police academy, part of Peace Officer Standards and Training, known as POST.
Maj. Scott Stephenson, POST’s director, said the 21-foot rule is not officially in the curriculum but added that he’s not surprised it would still be mentioned by his trainers.
“It effectively demonstrates that a dangerous person can cover at least 21 feet before most officers can draw their weapon,” he said. “It has also been part of police training culture for a long time.”
Salt Lake City police taught the 21-foot rule to journalists as part of a use-of-force training in 2017, but department spokesperson Brent Weisberg said recently that it’s a guideline — not a policy — for the department.
“The SLCPD Training Unit shares this guidance with academy cadets as a reference to demonstrate how much distance can be gained on an officer within a short period of time before a reaction is made,” he said in a statement. “Cadets are instructed to be mindful of the distance between them and an armed suspect, and to be cognizant of creating more distance or seeking cover between them and the suspect, if possible.”
Some specialized trainers are starting to provide alternatives.
At a recent crisis intervention training for Davis County police officers, licensed psychologist Todd Soutor brought up the drill.
“What’s the distance that you guys are taught to be away from [someone?]” he asked a room of officers.
“Twenty-one feet,” an officer quickly replies.
“Is there ever a time when someone has a knife where you would rather be 10 feet away than 21 feet away?” Soutor asked.
“If it’s a butter knife and you’re making a peanut butter sandwich,” one officer responded.
Soutor asked them to think about it differently. Maybe 10 feet is a safe distance, if there are chairs and obstacles between an officer and a subject, and space for an officer to back up. He called this “artificial distance.”
“It’s something to think about,” he told the police. “That’s an illustration of real distance. Twenty-one feet when you’re lined out on a straight path with no obstacles versus artificial distance.”
A justification for police shootings
On a March evening in 2019, a person called police to report a man and woman having a loud argument outside their Harrisville apartment.
When the three officers got to Jamal Bell’s home, they found the front door damaged. Body camera footage shows the officers pushed the door open, shined a light inside and asked if anyone was home.
No one responded at first, until Bell emerged with a knife in each hand. He sauntered toward the officers, the footage shows, as they backed up and yelled for him to drop the weapons.
One officer tried to fire a taser, but Bell slammed the door shut before the electrified probes could hit him. One of the officers then kicked open the door and the officers continued to order Bell to drop the knives.
The footage shows Bell raising his arms to his sides, teetering from one foot to the other.
“Take another step closer and I will shoot you!” one officer shouted. “I will shoot you!”
Bell stepped into the doorway, within feet of the officers. Just a few seconds later, three officers opened fire, striking Bell nine times.
Less than six months later, police officers in Weber County again were confronted with a man with a knife, this time in Ogden.
There, a neighbor called Ogden police Aug. 26, 2019, to report a man acting strangely.
“I tried to talk to him,” the man told the dispatcher. “He’s not really responsive. He looks very confused and then he has a knife pulled out.”
That man, Jovany Mercado, had been diagnosed with schizophrenia and when he was having an episode, he would hear things or become emotional and easily confused. He went from the street back to his house. Footage from the family’s security camera showed Mercado acting like he was talking to someone, but no one was there. He was wiping away tears.
Officers found Mercado behind the family carport. The security camera footage showed police told him to drop the knife. He didn’t and moved the knife from one hand to the other as he walked slowly through the structure, heading toward the opening in the chain link fence.
Four officers fired. He was hit 16 times and died.
In both cases, Weber County Attorney Chris Allred cited the 21-foot rule as one reason these shootings were legally justified.
In Bell’s case, Allred wrote that an officer told investigators he was specifically thinking of a training video.
“[The officer] said that every time in this training the officer would be stabbed before he could get his gun drawn and fire,” Allred wrote. “This ‘21-foot rule’ is common training for police officers.”
Allred wrote nearly the same thing when ruling officers justified in shooting Mercado, saying it was a common scenario in role-based training.
“In one demonstration, officers had encountered a person with a knife and tried to retreat and kept retreating, therefore putting them at a tactical disadvantage,” he wrote. “An officer was taken hostage during this encounter due to the inaction of the initial officers.”
Allred said he referenced the 21-foot rule because it explained why officers were concerned for their safety because of the distance between them and the man with a knife.
“The evidence showed that the suspect had gotten very close to officers before they fired,” Allred wrote in an email. “And in both cases, proximity was only one of several factors used to evaluate whether it was reasonable, under the totality of the circumstances, for the officers to believe the use of deadly force was necessary.”
Salt Lake County District Attorney Sim Gill has ruled on more police shootings than any other Utah prosecutor in the past decade. He told The Tribune that officers have raised the 21-foot rule, but he said that doesn’t mean the officer automatically was justified in using force. He said an officer needs to have reasonably feared for his life or another when he pulls the trigger.
Gill said what tactics police are taught, such as the 21-foot rule, can be the basis of that fear, but that fear still has to be grounded in the “underlying facts and the totality of the circumstances of that particular situation.”
Critics say that the training should be changed. The focus, they say, should be teaching cadets to de-escalate an encounter.
That includes Bell, that man who was shot nine times. He said during a protest in 2019 that he felt the police would have shot at him no matter what, even if he had dropped the knives. He added that he never threatened the police and said he wanted them to get better training so a gun was not the only option.
Robert Sykes, an attorney who represents Mercado’s family, said in 2020 that Ogden officers had ample opportunity to de-escalate the encounter or use less-than-level force. His family is now suing Ogden police.
“I know a knife can be a deadly weapon, certainly can be,” Sykes said. “But they had plenty of time to tell him to stop or I’ll shoot. They had lots of options. They didn’t have to kill this young man.”
FRONTLINE reporters Taylor Eldridge, Muna Mohamed and Abby Ellis and Tribune reporter Paighten Harkins contributed to this report.
This story is part of a collaboration with FRONTLINE’s Local Journalism Initiative, which is funded by the John S. and James L. Knight Foundation and the Corporation for Public Broadcasting.