NEW YORK (Reuters) - The maker of the Taser says the electroshock weapon is the safest tool on a police officer’s belt – with a few caveats.

In pages of warnings, Axon Enterprise Inc advises police to beware that some people are at higher risk of death or serious injury from the weapons. Pregnant women. Young children. Old people. Frail people. People with heart conditions. People on drugs or alcohol. The list goes on.

Taken together, the tally of people particularly susceptible to harm from a Taser’s powerful shock covers nearly a third of the U.S. population, a Reuters analysis of demographic and health data found. Yet police have repeatedly used Tasers on people who fall into the very groups the company warns about.

Dailene Rosario was one of them. Last winter, a New York City police officer fired his Taser’s electrified barbs into the rib cage of Rosario, 17, as she screamed she was pregnant. Thanks to a viral video taken by a bystander, the world watched as Rosario, 14 weeks into her term, crumpled to the ground, wailing.

What happened afterward has not been told.

Rosario’s daughter Raileey survived. But the baby is not faring well. In September, Rosario said, the two-month-old was rushed to the hospital, struggling to breathe after developing tremors and coughing fits. Raileey spent nearly all of November at Children’s Hospital at Montefiore in the Bronx, undergoing tests for a possible seizure disorder.

“Now it happens so frequently,” Rosario said of the tremors. “We can only just monitor her and try to keep her relaxed.”

Her lawyer, Scott Rynecki, said he plans to make the baby’s health a central issue in a $5 million legal claim she has filed against the New York Police Department. The NYPD said the incident remains under investigation and declined to comment further.

There’s no telling how often police use Tasers on pregnant women and the other “higher-risk populations” the manufacturer warns about: The stun guns are unregulated as police weapons, and there is no national tracking of their use.

Yet people in those groups account for more than half of the 1,028 cases identified by Reuters in which people died after being shocked by Tasers, often along with other force. Such people, Axon’s warnings say, should be targeted “only if the situation justifies an increased risk” of injury or death.

Particularly vexing for police is the difficulty of determining which potential Taser targets belong to population cohorts deemed to be at increased risk.

Some fatalities examined by Reuters involved people who obviously fell into a higher-risk category. Four, for instance, involved people over 75.

Yet many others involved vulnerabilities difficult to spot, particularly in the chaos of confrontation. Some 245 had a heart condition. And 643 people were drunk or high on drugs – a state often, but not always, easy to identify.

“People don’t walk around with signs” listing their medical conditions, said James Ginger, a former Evansville, Indiana, policeman now working as a consultant and court-appointed monitor of police compliance with judicial orders. The Taser is an important police tool, Ginger said. But if officers avoided anyone who potentially has a higher-risk condition, “you couldn’t use it.”

Axon calls Tasers the “safest force option available to law enforcement.”

The company told Reuters its warnings and training “do not identify any population group as ‘high risk,’ rather, they recognize that certain people may be at increased risk during encounters requiring force, regardless of the force option chosen.”

But the warnings issued to police by Axon, formerly known as Taser International Inc, note explicitly that “some individuals may be particularly susceptible to the effects” of its weapons. They identify an array of “higher-risk populations” and other vulnerable groups.

Law enforcement began embracing Tasers in the early 2000s. The manufacturer began listing higher-risk populations in 2009, when it also warned of possible cardiac effects from shocks to the chest. The list grew in the next few years.

Many in the police community say Tasers nevertheless offer a valuable option for controlling combative subjects without resorting to firearms. “There have been instances where we have saved a person’s life by using this piece of equipment,” said Virginia Beach Police Chief James Cervera. But as warnings on the weapons’ risks have evolved, he added, the department has “tightened up” on their use.

Axon’s warnings and guidelines are not binding on police departments, and while more than 90 percent of police agencies deploy Tasers, there are no universal standards for usage.

The uncertainty raises a challenge, some in law enforcement say. If large swaths of people are potentially at higher risk of death or serious injury from a Taser, how can police ever be sure the weapons are safe to use?

Nearly 80 percent of the population could fit into one of the higher risk groups identified by Taser’s maker, Reuters’ analysis shows. For example, any woman of childbearing age – about 20 percent of the population – could be pregnant. Any adult male could have impaired heart function, another third of the populace.

Police often have mere seconds to weigh such factors, said Chuck Wexler, executive director of the Police Executive Research Forum, a think tank that advises police on policy issues, including use-of-force. As a result, he said, “the Taser may be the most complicated weapon that a police officer wears today.”

A BIG HEART

Michael Mears, 39, was found on the floor in a hallway at his Los Angeles apartment complex on Christmas Eve 2014, bloodied and crying: “Help me. Help me.”

The police called to help the disabled veteran shocked him repeatedly with a Taser.

Mears had a vulnerability the officers couldn’t see: an enlarged heart.

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In 2009, the manufacturer introduced the possibility that Taser shocks could affect the heart. By Christmas 2014, it had warned that “serious complications could also arise in those with impaired heart function.”

That didn’t protect Mears, nor many others like him. Of the 750 Taser-involved deaths in which Reuters obtained autopsy information, 245 involved people with pre-existing heart problems. And of the 159 cases in which coroners ruled the Taser shock caused or contributed to the death, 68, or 43 percent, involved cardiac conditions.

Mears grew up in Florida and joined the Marines after high school. At 19, he helped evacuate United Nations troops from Somalia in 1995.

He injured his back in a shipboard fall two years later, said his mother, Joanna Wysocki. Surgery to repair his spine instead left him unable to walk. After years of rehabilitation, he had begun to walk again. But he often lost feeling in his weakened legs and needed a walker or wheelchair.

Wysocki said she talked to her son by phone the morning of his death, and he was excited about having friends over for Christmas Eve dinner. But that afternoon, he began acting strangely, court records show.

He rolled a candlestick across the floor as if he were throwing a grenade, and then ran out of the apartment. A neighbor peeked through a door and saw him lying on the floor, crying for help, she told detectives. Mears was covered in blood from rolling in shards of glass from a broken fire extinguisher case.

“He has PTSD,” a friend told the paramedics who arrived. Several LAPD officers followed. The first two hit Mears with pepper spray and batons because, the autopsy report said, he appeared combative.

The Taser’s log shows Mears was shocked six times totaling 53 seconds over three minutes. The longest: 32 seconds. Taser guidelines advise officers to avoid “repeated, prolonged or continuous” shocks, noting that safety testing typically involved no more than 15 seconds of exposure.

The officer who stunned Mears testified he believed he was applying 5-second shocks and had no idea his Taser delivered electricity for as long as he held the trigger. The LAPD declined to discuss the case or make the officer available for comment.

The Los Angeles County Medical Examiner-Coroner ruled Mears’ death a homicide, concluding that cocaine and police efforts to restrain him, including the Taser shocks, were too much for his heart.

His parents sued the city. Jurors blamed the city for being “deliberately indifferent” to officer training and awarded them $5.5 million.

Mears died Christmas morning, while his mother was flying from Florida. “I’ll never get to say goodbye,” she said.

NURSING HOME TRAGEDY

Sometimes, the vulnerabilities are more obvious.

There was no mistaking Stanley Downen was elderly when Columbia Falls police answered a call from the Montana Veterans’ Home for help with a wandering resident in June 2012. Downen, 77 with advanced Alzheimer’s, was just outside the gate, circled by several staffers urging him to come back inside.

A retired ironworker and Navy vet, Downen had scooped up landscaping rocks, one as big as a softball, and was threatening to throw them at anyone who came near. Officers Mike Johnson and Gary Stanberry approached, asking him to put down the rocks.

Downen cursed at the officers and said he wanted to go home.

They tried again; same response.

Johnson drew his Taser and fired. He later testified that Downen had reared back as if to throw one of the rocks. “I believed that I was going to be physically harmed.”

Paralyzed by the Taser’s electrified darts, Downen’s body seized and he fell forward, his head smacking the pavement. Handcuffed, he continued cursing and struggling.

Downen was taken to a nearby hospital, but his dementia worsened. He died there three weeks later.

Axon has warned since 2008 about using its weapons on “elderly” people and advises that doing so “could increase the risk of death or serious injury.” A model Taser policy from the Police Executive Research Forum includes similar warnings.

But neither designates an age threshold for “elderly,” and dozens of police department policies reviewed by Reuters specify no age limit.

Reuters identified 13 cases in which people 65 and older – the eligibility age for Medicare – died after being stunned by police with Tasers. All but two occurred well after the manufacturer’s first warnings.

By the time Columbia Falls police confronted Stanley Downen in 2012, the warnings had been in place for years. Officer Johnson later testified he never saw them.

In depositions and court records from a lawsuit filed by Tamara Downen, Stanley’s granddaughter, Johnson and the police department acknowledged he had not been trained or certified on Taser use since 2006 – two years before the manufacturer first warned against shocking the elderly. Officers are supposed to be re-trained and certified on the weapons annually, according to guidelines from the manufacturer and independent law enforcement groups.

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The department also had no formal policy on Taser use, court records show, and its procedures manual never mentioned the weapon.

Tamara Downen sued the state-run nursing home and city police, alleging unsafe practices and improper Taser use in her grandfather’s death. “It just wasn’t right, what he went through,” she said. The city settled for $150,000; the state for $20,000.

Columbia Falls later hired a new police chief, Clint Peters. Citing the litigation, he declined to comment on the case or make the officers available for interviews. But he said the force now has a Taser policy based on guidelines from national law enforcement groups.

‘TOTALLY INTOXICATED’

Axon has warned since 2005 that people agitated or intoxicated by drugs may face higher risks of medical consequences from Tasers’ electrical current. Data collected by Reuters underline that risk: More than 60 percent of 1,028 people who died in police confrontations involving Tasers were either drunk or on drugs.

Some who died were unmistakably intoxicated – like Doug Wiggington.

In Greenfield, Indiana, last May 12, Wiggington stumbled out of the local Elks Lodge just after 6 p.m., falling as he walked near a two-lane highway. James Fornoff, 74, called police. “He had no clue what he was doing,” Fornoff said.

When the first officer arrived at 6:27 p.m., Wiggington, 48, was lying in the grass, wiggling his feet, police dash-cam videos showed. “What have you taken?” Officer Dillon Silver asked.

As officer Rodney Vawter joined him, Silver rolled Wiggington onto his side, patting him down. Silver began to pull him onto his back but Wiggington stiffened. Silver grabbed his arm, saying, “Do not tense up on me.” Wiggington, 6 feet and 230 pounds, rolled onto his stomach.

“Tase him,” said Silver. Vawter pulled the trigger and the barbs struck Wiggington’s back. He writhed and grunted. “I’m going to do it again if you don’t listen!” Vawter said. The struggle continued. Vawter fired again.

When the officers turned him over, Wiggington was unconscious. They gave him two shots of Narcan, an overdose antidote for opioids, and started CPR. When the ambulance arrived, Wiggington had no pulse. Thirty minutes later, he was pronounced dead.

The autopsy said Wiggington died from “acute cocaine and methamphetamine intoxication.” The Taser was listed first among contributing factors.

“We have a lot of unanswered questions,” said Wiggington’s daughter, Brittany, 30, who has filed legal notice of her intent to sue the department.

By the time Wiggington was shocked, the company’s training materials had noted explicitly for years that Tasers cause “physiologic and/or metabolic effects that may increase the risk of death or serious injury” – and drug users “may be particularly susceptible.”

None of that language appeared in the Greenfield Police Department’s Taser policy at the time. The officer who shocked Wigginton, Vawter, hadn’t been re-certified on the Taser in more than three years.

Greenfield Police Chief Jeff Rasche said the two officers did not violate department policy and were cleared by an internal investigation and a separate state probe. Axon, he added, does not explicitly bar using the weapon on people under the influence of drugs or alcohol, but instead warns of the risks.

Rasche, chief since last January, said he had ordered his 42 officers to undergo a six-hour Taser re-certification class before the death. At the time of the incident, nine had completed it. Vawter wasn’t among them.

Since the death, Rasche has ordered all officers to undergo “crisis intervention training,” emphasizing de-escalation strategies in lieu of using force such as Tasers.

“We can’t just do the same thing we’ve been doing forever because it’s not working,” the chief said. “People are unfortunately dying and officers are having to use lethal force when they, you know, probably shouldn’t be.”

THE PREGNANCY PROBLEM

At any given time, 6 percent of women of childbearing age are pregnant. But, in the early stages, the signs of pregnancy are rarely obvious.

Since 2003, Axon has warned that pregnant women are at particular risk of injury from falls after being shocked. Still, the company suggested then that the weapons’ electrical charge posed no other special risks to women or fetuses. In 2004, it cited lab tests in which an electric charge was delivered to the abdomens of pregnant pigs with “no adverse effect on fetuses.”

In 2009, Axon identified pregnant women as a “higher risk population.” By 2011, news reports described nearly a dozen women who had suffered miscarriages or other pregnancy complications after stun-gun shocks.

Definitively measuring the risks of shocking a pregnant woman is impossible: There has never been a controlled study of the Taser’s effects on pregnant women. Such tests, by their nature, are too risky to undertake.

Yet since electricity is a known cardiac hazard, doctors theorize it poses some risk.

“There may be an instantaneous fetal effect when the Taser discharges, but you may not know about that until when he is a small child,” said Michael Cackovic, an obstetrician who heads the maternal cardiac disease program at the Ohio State University Wexner Medical Center.

Cackovic said risks from a Taser shock include disrupting the flow of oxygen from the mother, potential fatal cardiac arrhythmia, damage affecting the brain and other problems that may emerge years after birth.

No government authorities track miscarriages or other problems linked to pregnant women stunned by Tasers. A Reuters review of court filings and news articles found 19 incidents of women stunned while pregnant, at least 11 of which were followed by a miscarriage, since 2001.

One such case played out on a hot August morning in Lima, Ohio, in 2016. Brittany Osberry, 24, stumbled into a crime scene as she pulled into her friend’s driveway to pick up her nieces and nephews. Police were monitoring the home because they mistakenly thought a suspect in a shooting may be inside. Within seconds, three officers swarmed her car.

“You need to leave!” officer Mark Frysinger shouted, gun drawn, the altercation captured on a neighbor’s cellphone. “This is a crime scene.”

When she asked why, Frysinger accused her of disorderly conduct and told her to leave again. She protested: She wanted first to pick up the children. The officers moved in. “Show me your hands,” Frysinger yelled, pulling her from the car. Three officers pushed her up against the door.

“You all better know I’m pregnant,” she shouted. “You all better know that.”

One officer put her in a choke-hold and lifted the 104-pound woman back so high the tips of her toes touched the driveway. Another officer, Zane Slusher, drove a Taser into her abdomen. “Oh my God!” she screamed.

In an incident report, police said Osberry was combative and struck an officer – assertions a federal judge said were “not conclusively” borne out by the video. Osberry was arrested for obstructing official business, resisting arrest, disorderly conduct and assault. The charges were later dismissed. No official reason was given.

Within hours, she said, she felt stomach cramps. A month later, ultrasounds couldn’t detect the baby’s heartbeat. Other tests found a beating heart, but her doctors identified another problem: Osberry was suffering from preeclampsia, a dangerous spike in blood pressure during pregnancy that can interfere with blood flow to the placenta and fetus.

She underwent tests twice a week. The fetus wasn’t gaining weight.

Then, that New Year’s Eve, with Osberry 30 weeks pregnant, her doctor said the baby was coming. Contractions began and the baby’s heartbeat plunged, she said. On the way to the hospital, she wept, “not knowing if I would lose him.”

Kannon was born at 2 pounds, 2 ounces and stayed at the hospital nearly two months. Today, he’s generally healthy but struggles to use his left leg; doctors aren’t sure if he’ll face long-term developmental problems.

In February, Osberry filed suit against Lima Police and the officers involved. The department said it had “probable cause” to arrest her and cited “qualified immunity,” a concept providing legal protection to officers unless police violate “clearly established’’ legal principles.

In November, a federal judge rejected the department’s attempt to have the case dismissed. Lima Police have appealed the ruling.

“Given the factual allegations, I am hard-pressed to imagine a scenario less deserving of qualified immunity,” wrote U.S. District Judge James Carr. A “reasonable officer,” he said, should know not to use a Taser on a “non-resisting pregnant woman.”