(CNN) He hid his face, but "Jihadi John" was the English-speaking voice of ISIS. His twisted, videotaped taunts and acts of terrible cruelty -- beheading hostages who had gone to the Middle East to report stories and help others -- symbolized the Islamist militant group's depravity and ruthlessness.

Not anymore, it appears.

U.S. Army Col. Steven Warren said Friday that a drone strike the previous night killed everyone in the targeted vehicle, with Mohammed Emwazi -- a.k.a. "Jihadi John" -- likely among them.

"We are reasonably certain that we killed the target that we intended to kill, which is Jihadi John," the Army spokesman said. "...This guy was a human animal, and killing him is probably making the world a little bit better place."

The United States had been tracking Emwazi closely since Wednesday, and he was seen leaving a building and getting into a car Thursday, U.S. officials said. Three drones went after that vehicle, which also had another person inside, and two Hellfire missiles were fired.

Raqqa is Being Slaughtered Silently, a Syrian activist group, said a missile hit Emwazi's car directly at 11:51 p.m. (4:51 p.m. ET) in front of an ISIS court in Raqqa. Citing a source in ISIS' de facto capital, the same group said that ISIS militants then ringed that vehicle and two others that had been struck to prevent anyone from getting closer.

Speaking hours later Friday, British Prime Minister David Cameron cast the airstrike as an act of self-defense that, if it is confirmed Emwazi is dead, "will strike at the heart of ISIS."

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"We always said we will do whatever is necessary to track down Emwazi and stop him taking the lives of others," he said.

But there is no joy or sense of victory from Louise Woodward-Styles. Her friend, British aid worker David Haines, was among the hostages whose beheading videos featured Emwazi. Others included American journalists Steven Sotloff and James Foley, U.S. aid worker Abdul-Rahman Kassig, British aid worker David Haines and Japanese journalist Kenji Goto.

"There's just sadness," Woodward-Styles said. "It reminds you of the loss of Alan and just hoping it's closure for the family. But also I hope it reminds people that the issue of Syria is still ongoing, and not to forget the reasons why Alan was there."

As to Emwazi himself, Woodward-Styles added, "I don't think he deserves the attention that his apparent death is causing. I think he was a coward."

Justice for 'victims of this evil man'

As the masked face of ISIS , the British citizen appeared in a series of brutal videos, dressed head-to-toe in black -- his eyes and voice his lone revealing features -- and holding a knife.

The Ramadhan Foundation, a Muslim organization in the UK, called Emwazi the manifestation of evil.

"The killing of Mohammed Emwazi in Syria is a significant moment in the fight to get justice for David Haines, Alan Henning and all the victims of this evil man," said Mohammed Shafiq, the group's executive director.

That sentiment wasn't shared by CAGE, the London-based civil rights group that had contact with Emwazi. The group stated "its opposition to extrajudicial killing of any kind," adding that "state-sponsored targeted assassinations undercut the judicial processes that provide the lessons by which spirals of violence can be stopped."

Rather than be killed, CAGE said, Emwazi should have been tried as a war criminal. Because that won't happen, the world will never know what spurred him -- and many others in the West and beyond -- to join ISIS.

His killing means key crucial questions around his joining ISIS, as well as the kidnapping and killing of hostages will remain unanswered. — CAGE (@UK_CAGE) November 13, 2015

"His killing means key crucial questions around his joining ISIS, as well as the kidnapping and killing of hostages will remain unanswered," CAGE tweeted.

U.S. official: Blow to ISIS' prestige

Syrian activists in Raqqa reported that four ISIS foreign fighters, including a leader with British nationality, were killed by the coalition airstrike, the Syrian Observatory for Human Rights said.

If that British leader is Emwazi, it would be a significant step in the anti-ISIS fight for the West -- not necessarily on the ground, with U.S. military spokesman Warren saying he wasn't "a major tactical figure," but symbolic, given his part in recruiting efforts and the terror group's overall public image.

"Jihadi John was somewhat of an ISIL celebrity," he said, using another common acronym for the group. "... So there is a significant blow to (the group's) prestige."

His rapid rise in prominence paralleled that of ISIS itself, which was born in post- Saddam Hussein Iraq and burst into prominence in the midst of Syria's ongoing civil war . While a number of groups have been in that fight, none have had the success of the entity that calls itself the Islamic State. The group's mercilessness, epitomized by "Jihadi John," against any who don't submit is a major reason for those inroads.

In the process, though, ISIS has raised urgency among an array of parties -- from the United States and its allies, to Russia and the Iraqi and Syrian governments -- to thwart the group, ideally to crush it.

Arrests -- like one this week in Turkey of another British member of what tabloids have called the "Beatles" cell, according to U.S. officials -- are one part of the effort to corral ISIS. So, too, are coalition airstrikes, with Warren estimating they've killed at least one mid- to high-level ISIS figure every day since May.

"I don't think they're gaining strength," President Barack Obama told ABC's George Stephanopoulos in an interview that aired Friday morning. "... We have contained them."

Emwazi's radicalization

By his own account, Emwazi was born in Kuwait, and it is believed he moved to London as a child. Friends say they think he started down the road to radicalization when he traveled to Tanzania in 2009, The Washington Post reported this year.

He was supposed to be going on safari in the East African nation, but he was reportedly detained on arrival, held overnight and then deported. He was also detained by counterterrorism officials in Britain in 2010, The Post said. Authorities have not disclosed the reasons for those reported detentions.

"I had a job waiting for me and marriage to get started," he wrote in a June 2010 email to Asim Qureshi, a member of CAGE , The Post reported. "(But now) I feel like a prisoner, only not in a cage, in London. A person imprisoned & controlled by security service men, stopping me from living my new life in my birthplace & country, Kuwait," the email said.

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Emwazi is believed to have traveled to Syria in 2012 and joined ISIS there. He soon became a regular in hostage videos and participated in beheadings.

For some periods of time this year, Emwazi was not seen in videos, though U.S. officials told CNN in July they had learned he was alive and hiding near Raqqa. He may have been laying low for fear of being targeted, though the U.S. government believes he remained involved in kidnapping and killing cells.

Analysts describe him as grotesque and fond of sadistic torture techniques, with one former hostage recounting last month how his captor made him dance the tango with him

"Suddenly, he changed and just pushed me down," Daniel Rye, a 26-year-old photographer, recalled to Danish broadcaster DR. "They kicked and hit me. They finished by threatening to cut my nose off with pliers and things like that."

Speaking to Japanese state broadcaster NHK, Junichi Goto speculated on whether his brother, slain hostage Kenji Goto, might be alive today if the airstrike had happened earlier, though realizing that ISIS' deeds can't be reduced to just one man.

"ISIS continues to kill hostages in the same way it did to Kenji," Junichi Goto said. "I wish no repeat of the tragedy. And I wish ISIS would disappear."