GEOFF BENNETT: Ever since a police officer fatally shot 18-year-old Michael Brown in Ferguson, Missouri, almost nine years ago, police use of force against people of color, especially Black Americans, has been under intense scrutiny.

Much of the attention is on firearms, but types of force considered to be less lethal, like choke holds and Tasers, are also getting a closer look.

As John Yang reports, Tasers may rank below guns on the spectrum of police force, but using them has resulted in deaths.

A note that some images in this report are disturbing.

JOHN YANG: Sonya Williams struggles with the death of her first-born child, Darryl Tyree Williams.

SONYA WILLIAMS, Mother of Darryl Tyree Williams: He was a good person.

You know what I'm saying?

I'm not going to say that he was perfect.

He had his flaws, like we all do.

But he was loved by everyone.

He didn't have no enemies.

JOHN YANG: She's especially troubled by the way Darryl died, in the custody of police who had used a Taser on him several times.

SONYA WILLIAMS: He didn't deserve this.

A don't day go by I don't think about him.

It's just hard.

It's a hard thing to go through.

JOHN YANG: The events leading up to Darryl Williams' death began unfolding at about 2:00 a.m. on a January morning.

Williams was sitting in a parked car on Raleigh, North Carolina's southeast side.

Police were in the predominantly Black neighborhood on what they call proactive patrol, because, they said, officers are frequently called to the area.

In Williams' pants pocket, an officer finds a folded $1 bill with a white powdery substance.

POLICE OFFICER: Put your hands behind your back.

DARRYL TYREE WILLIAMS, Died in Police Custody: Why?

POLICE OFFICER: Both hands behind your back.

DARRYL TYREE WILLIAMS: Why?

JOHN YANG: There's a struggle as Williams tries to get away.

The officer draws his yellow Taser and fires.

Its probes make contact with Williams and deliver an electrical charge designed to temporarily paralyze him.

Williams momentarily breaks free and is Tased again.

POLICE OFFICER: Behind your back.

JOHN YANG: With officers holding him down, Williams pleads with them.

DARRYL TYREE WILLIAMS: I got heart problems.

POLICE OFFICER: You're going to get Tased again.

POLICE OFFICER: Put your hands behind your back.

POLICE OFFICER: Put your hands behind your back.

SONYA WILLIAMS: Please.

Please.

POLICE OFFICER: Three, two, one.

(SCREAMING) JOHN YANG: In all, officers had Tased Williams four times.

About an hour later, Williams was pronounced dead at a hospital.

He was 32 years old.

An autopsy concluded that Williams died from sudden cardiac arrest in the setting of cocaine intoxication, physical exertion, conducted energy weapon use, and physical restraint.

The death was ruled a homicide.

DAWN BLAGROVE, Emancipate North Carolina: Darryl Williams lost his life because the Raleigh Police Department apparently doesn't have anything better to do than to harass Black and brown people.

JOHN YANG: Dawn Blagrove is executive director of Emancipate NC, a North Carolina group that focuses on race and policing in mass incarceration.

She's also one of the lawyers representing the Williams family.

She underscores the role of the Taser in Williams' death.

DAWN BLAGROVE: It can be a deadly weapon, in the hands of Raleigh Police Department officers, clearly, because Darryl Tyree Williams is no longer with us.

JOHN YANG: There is no authoritative database of deaths that follow the use of a conducted electrical weapon.

But a 2017 investigation by Reuters put the tally at more than 1,000, nearly all of them since the early 2000s.

KALFANI TURE, Widener University: They classify them as less lethal today, because the lethality is still present.

JOHN YANG: Kalfani Ture is a professor of criminal justice at Widener University and a former police officer.

He says police shouldn't use Tasers since officers can't know if a target has health problems.

KALFANI TURE: We're not trained as medical experts.

When we train to use Tasers, we simply train around the mechanical parts of it.

JOHN YANG: Tasers are by far law enforcement's most commonly used conducted energy weapon.

Its manufacturer, Axon, wouldn't speak with us on camera, but materials the company provided cite findings of independent studies that 99.75 percent of incidents in which a Taser was used did not result in serious injury, and that, of the tools available to police to exert force, a Taser is least likely to result in significant injury, less likely even than unarmed physical force.

The lead author of both studies is Dr. William P. Bozeman, an emergency medicine professor at Wake Forest University School of Medicine.

He says his work is not funded by Axon.

DR. WILLIAM P. BOZEMAN, Atrium Health Wake Forest Baptist: When it comes to cardiac effects, it's extremely rare.

And the current estimate is one in 2 to 2.5 million.

JOHN YANG: Bozeman says decades of research on Tasers have established that they are safe, even if there are rare instances in which they contribute to a death.

DR. WILLIAM P. BOZEMAN: A Taser can absolutely kill you.

Whether it can do that by a cardiac means is still a topic of discussion.

But there have clearly been cases where people were standing in an elevated position, and they were struck with a Taser, and the muscular lockup occurred, and they fell and they had a major head injury, and they died.

But Tasers are actually remarkably safe.

MIKE GISH, Vice President of Taser Product Management, Axon Enterprise: We owe public safety and communities a better way to stop threats without having to take a life.

JOHN YANG: That's Tasers' key selling point.

Axon estimates that about 285,000 lives have been saved or serious injuries prevented because police used their devices, instead of a gun.

Raleigh attorney Dawn Blagrove says Tasers may be a useful tool, but the issue is how police use them.

DAWN BLAGROVE: The reality is, we need an entire paradigm shift around when force is necessary for law enforcement, even if it is nonlethal weapons.

If it is used with the intent to cause harm, to cause pain, to punish someone, that is always going to result in the people of Raleigh and anywhere else being in danger of death for even simple interactions with law enforcement.

JOHN YANG: In June, Wake County district attorney Lorrin Freeman announced that she was not bringing criminal charges against any officers in connection with Williams' death.

LORRIN FREEMAN, Wake County District Attorney: Yes, I would say this is one of the cases that I personally have struggled with more than others, candidly.

JOHN YANG: Among the circumstances she says led her to her conclusion, what she calls the limited uses of Tasers on Williams, none longer than five seconds, the question of whether officers heard Williams tell them about his heart condition, and the complications posed by the autopsy report, which cited a combination of factors contributing to Williams' death, rather than a single cause.

LORRIN FREEMAN: At the end of the day, the law enforcement actions while difficult to watch, while leading to a very tragic end, were lawful and in some instances were what were necessary at that point in time to bring the situation under control.

And so, hopefully, we learn from these situations kind of on both sides of that interaction.

JOHN YANG: Six officers involved in Williams' death were placed on paid administrative leave.

The Raleigh Police Department declined an interview request and wouldn't go beyond a written statement.

It said it is department policy that: "A conducted energy weapon shall only be used in response to active resistance."

The statement adds: "It is important to note that our officers are required to make split-second decisions in quickly evolving circumstances."

DAWN BLAGROVE: Darryl was not trying to harm law enforcement.

He did not pose a physical threat.

He was trying to get away.

He was trying to save his own life.

Ultimately, without the intervention of other human beings, namely, the Raleigh Police Department, Darryl would not have died on that night.

If this were some random non-law enforcement citizen who had committed a crime that resulted in the death of someone else, that person would be charged.

JOHN YANG: The DA's decision also frustrates Darryl's mother, Sonya.

SONYA WILLIAMS: I don't have anything against the Tasers.

I just think it's the way they use it.

They used excessively on my child.

And until something be done about it, they're going to keep on doing it.

JOHN YANG: Now that the district attorney has decided not to do anything, Sonya Williams and her attorney said they are exploring their options in their pursuit of accountability for the police and justice for Darryl Tyree Williams.

For the "PBS NewsHour," I'm John Yang.