When US President Joe Biden announced he had tracked down and ordered the CIA to kill Ayman al-Zawahiri, he stressed every effort was made to avoid collateral damage.
The 71-year-old Al Qaeda leader, who died on July 31, was killed in a drone strike as he stood on his balcony in downtown Kabul.
The White House said it only wanted Zawahiri dead — not his family members who were also in the house, or any neighbours living nearby.
"[Joe Biden] was particularly focused on ensuring that every step had been taken to ensure the operation would minimise that risk," a senior administration official told journalists in a private background call.
And so officials said they used two Hellfire precision guided missile shot from an unmanned drone.
By America's standard, the operation was a success: Zawahiri was the only person killed.
But new pictures of what is purported to have been the Al Qaeda leader's home have intrigued military experts.
While online images show some damage to the balcony, there is hardly a scratch on the rest of the building — no rubble and no scorch marks.
It has left many counterterrorism analysts wondering if America deployed a brutal weapon that does not involve explosives at all.
Instead, some suspect the CIA might have used the Hellfire R9X — a highly secretive missile sometimes called the "knife bomb", the "ninja bomb" or the "flying Ginsu" because it uses a series of rapidly spinning blades to kill.
The US missile that has been shrouded in mystery
Hellfire missiles are known for their precision and mobility, making them a useful weapon in America's military arsenal for the past 20 years.
They can be mounted on helicopters, ships, ground vehicles or on unmanned drones.
Some models can "do enough damage to destroy most targets — such as vehicles and buildings — while not doing enough damage to level city blocks and cause significant civilian casualties", Ryan Brobst, an analyst at Washington think tank Foundation for the Defense of Democracies, told The Associated Press.
But when it comes to the assassination of Zawahiri, some experts and counterterrorism sources believe the US may have used a modified Hellfire missile dubbed the R9X.
Its existence has been a source of speculation and intrigue for years, with very little information about the modified version being made publicly available.
What is known is that unlike conventional missiles, the R9X does not explode when it hits its target.
Instead, it has six razor-like blades that are released from the skin of the missile and rotate at high speed, moments before impact.
It can cut through metal, such as cars, and plunge through buildings without damaging nearby property.
"One of their utilities is in opening up vehicles and other obstructions to get to the target without having to use an explosive warhead," Klon Kitchen, senior fellow at the American Enterprise Institute and a former intelligence analyst, told AP.
When the missiles are used via a drone, sophisticated cameras display a video stream of the target to a weapons operator located some distance away.
Once the mark is identified, the operator can point a laser to help guide the missile to its target after it has been dropped.
The complicated history of American missile strikes
The Hellfire R9X is highly sought after for lone targets because of its ability to cause less damage than its predecessors.
The modified missile was reportedly the result of former president Barack Obama's emphasis on reducing civilian casualties and property damage in America's wars on terrorism.
Precise missiles were also necessary once terrorist fighters adapted to US air strikes and started using women and children to keep themselves safe from fire.
Analysts first realised the US might have a new weapon in its arsenal in 2017 when Zawahiri's own deputy was killed in a very strange strike in Syria.
Ahmad Hasan Abu Khayr al-Masri was killed by a Hellfire missile while driving through Idlib province.
But instead of leaving a mangled, flaming wreck of the car, this weapon just sliced an oblong-shaped hole through the roof of the car.
Masri would have died instantly.
But other than a cracked windscreen and a gaping hole in the roof, the car was intact.
Two years later, another Zawahiri associate, Jamal Ahmad Mohammad al-Badawi, died in similar circumstances while driving alone in Yemen.
A mix of surveillance and intelligence
Since the Taliban took back control of Afghanistan last year when US forces left, it is believed many terrorists have returned to the capital and lived relatively luxurious lives.
The CIA never shares many details about how it finds, watches and kills foreign targets.
However, it appears that a tip-off led it to a house in the ritzy suburb of Sherpur in Kabul.
Undercover surveillance found that a family lived there, but the sole adult man never appeared to leave the house, according to the New York Times.
He did, however, spend a lot of time on the balcony, which gave the CIA the opportunity to confirm his identity and eventually kill him.
The use of a bladed weapon would have been "by far a lower-risk option", Tom Karako, an expert on missile defence at the Washington-based Center for Strategic and International Studies, said.
"It reflects a high degree of caution as opposed to a riskiness."
Experts were sceptical of the US' ability to watch over Afghanistan from "over-the-horizon" — through surgical strikes and special operations raids — after it withdrew its troops.
Yet Sunday's attack showed it was still able to carry out strikes from outside the country.
Innocent Afghan lives may have been spared this time, but human rights advocates have still expressed concern about the R9X.
"Part of the danger here is that these weapons seem so failsafe," Letta Tayler from Human Rights Watch told Bellingcat.
"But the R9X is only going to be as good as the intelligence used to guide it. Even if the US determines it wants to kill a particular person, that doesn't mean that it can legally do so."
