There's no magic in this bullet, but it saved 12 innocent lives—eight men and four women.

The single shot triggered an explosion that killed a top Islamic State (ISIS) executioner and three other jihadists, who were recording what was supposed to be another routine mass killing for the group's propaganda video, the Daily Mail reports.

The bullet reportedly came from a Barett .50-caliber rifle fired by a British Special Air Service (SAS) sniper who was posted nearly a mile away from the execution site near Raqqa, Syria.

The SAS shooter fired the shot just seconds before the executioner was set to burn the hostages alive using a flamethrower.

The bullet struck the fuel tank strapped on the back of the ISIS executioner, triggering an explosion that instantaneously killed him and his three fellow jihadists.

The unidentified executioner was a notorious ISIS militant who had been on a U.S. "kill list" for several months, according to the Daily Star. Reports said he and several other militants had been traveling around ISIS-held compounds in Syria killing civilians accused of being spies.

After receiving a tip on the executioner's location, British special forces tracked him to a town near Raqqa.

"The SAS team moved into an overwatch position above a village where they were told the execution was going to take place. Up to 12 civilians were going to be murdered—eight men and four women. They were suspected of being spies," a source told the Daily Star.

The source said none of the hostages were actually spies and that the ISIS militants knew that. Nevertheless, they decided to execute them "to instil fear into the local population," he added.

The SAS sharpshooter waited first for the executioner to finish his rambling speech over a loud hailer condemning the hostages. When he was about to set them on fire, the sniper let loose a single round from his rifle.

The shot hits the bull's eye, triggering a blast that reportedly killed all four ISIS militants at the scene. The hostages were presumably rescued following the botched execution.

SAS sharpshooters have been in action in Syria for quite some time. In May, British sniper killed an ISIS commander in Syria while he was teaching child soldiers how to decapitate enemies. Last December, an SAS sniper used only three bullets to take out five ISIS fighters in Iraq, according to the Daily Caller.