The Islamic State video depicting the brutal immolation of a Jordanian pilot was different from the start. The Islamic State has released numerous videos showing acts of barbarity including beheadings and mass shootings.

Those videos, often starring the masked militant known as Jihadi John, are sometimes rough and hurried. This one, by contrast, plodded through 22 long minutes. It had a narrative quality. There was building tension. And a clear message.

It revolved around a searing and unsettling new theme: Fire. The video showed snippets of news segments showing Jordan's involvement in the U.S.-led fight against the Islamic State before focusing on computer generated images of a "crusader" fighter jet firing missiles and a truck burning. The camera zooms in on charred corpses hidden under rubble. Each image bursts into flames.

Eventually, the video settles on Lt. Muath al-Kaseasbeh, walking across ruins, surrounded by militants. He enters a cage and is set alight. After he has been killed, rubble is tipped on his corpse by a front-end loader. In a broadcast on Islamic State-controlled radio on Wednesday, Kaseasbeh's fiery death was described as "punishment for what he had done of burning Muslims with the fire of his plane."

The use of immolation was especially shocking because it was so unusual -- burning someone to death is almost unheard of in the modern Middle East and throughout Islamic history -- and the killing sparked a theological argument. Clerics from the Islamic State quickly issued a fatwa to justify the killing, while other prominent clerics, such as the Saudi Sheik Salman al-Oudah, argued that immolation was prohibited by Islam.

"Many statements attributed to Muhammad condemn the practice, so ISIS guys have to rely on a Quranic verse to get around it," Will McCants, Director of the Brookings Institution's Project on U.S. Relations with the Islamic World, wrote in an email, using an acronym of the Islamic State. "Pretty shaky jurisprudence."

That Quranic verse (16:126) forms part of the basis for "qisas," a broad concept in Islamic law that calls for equal retribution for crimes -- in essence, an eye for an eye. As Shiraz Maher, a senior fellow at the International Center for the Study of Radicalisation at King's College London, writes, it's usually used in cases of murder or mutilation. At points, jihadist groups have used it to justify jihadists' attacks before: Al-Qaida later used the concept to justify a 1995 strike on the Egyptian Embassy in Islamabad, for example.

On Twitter, supporters of the Islamic State and other Muslims debated the use of qisas to justify what they saw in the video. "Teenage fanboys giving rulings on what qisas is and when it applies," wrote one critical user, dismissively.

Hassan Hassan, an analyst with the Delma Institute, a research center in Abu Dhabi, says that at best "qisas" can only be broadly applied by the Islamic State, as "it is not clear who was burned by the pilot or his country." Instead, the Islamic State repeatedly refers to "mumathala" (reciprocity), a broader term for dealing with enemy combatants. "The way ISIS justified the immolation of the pilot is the way it justifies many of its brutal acts," Hassan explained. "It relies on genuine but isolated incidents in Islamic history."

Hassan notes that the Islamic State pointed to the example of Khaled bin al-Walid, Muhammad's commander-in-chief, who burned "apostates" and that it also pointed to specific Islamic scholars who justified the use of immolation, such as al-Hafidh bin Hajar, a prominent Sunni scholar from the medieval era. These references may be obscure, but the fact that other Islamic scholars ignore them gives the Islamic State an upper hand, Hassan says. "By having monopoly over telling these stories, ISIS can shape them as it see fits to suit its brutal ideology," he explains. "Theology matters a lot in this context."

The use of immolation likely achieved another purpose: the introduction of a fresh form of terror. The most potent tool in the Islamic State's arsenal has been its willingness to push the boundaries of barbarity, which has attracted both global notoriety and a deluge of recruits. "'We've lopped off enough heads,' they might have said," Timothy Furnish, a historian of Islamic history who is frequently critical of the Islamic State, said in a phone call on Tuesday. "'Now, let's kick it up a notch and find a horrible way to kill this man.' "

It's not easy to continuously deliver shock value. The Islamic State's decapitations were utterly horrifying at the time of American photojournalist James Foley's death -- but do they impart the same effect today? Terror has a habit of escalating. Hijacked airliners gave way to suicide bombings. Suicide bombings gave way to decapitations and crucifixions and, now, immolations. It's disturbingly new, but also tragically familiar, The Washington Post's Philip Kennicott wrote on Tuesday. Horrific killings do more to transport us back to our civilization's roots than offer anything new.

"This isn't about mankind's macabre ability to invent new forms of murder; it's about reanimating our oldest, and collectively shared, habits of barbarism," Kennicott wrote. ". . . The Islamic State is not innovative in its depredations. Its thugs simply reach into the museum of human-made misery and pull out something at once horribly familiar, and terribly alien."