The beheading of Peter Kassig made the rounds on the internet and news media after ISIS released the video Sunday. The footage of the beheading of Peter Kassig showed a masked militant standing over the severed head of a man who the masked man said was of Kassig, a former U.S. Army Ranger-turned-aid worker.

Kassig was abducted while reportedly delivering relief supplies in Syria the previous year.

After seeing the video of the beheading of Peter Kassig which also showed the mass beheadings of a dozen Syrian soldiers, President Barack Obama confirmed its authenticity, describing the killings as "purely evil."

Kassig, 26, founded an aid group to help Syrians caught in the middle of their country's brutal civil war.

"He was taken from us in an act of pure evil by a terrorist group that the world rightly associates with inhumanity," Obama said in a statement.

The President also denounced the extremist group, saying they revel "in the slaughter of innocents, including Muslims, and is bent only on sowing death and destruction."

Meanwhile, Mirror reports that Kassig's parents, Ed and Paula, have spoken up the beheading of their son, Peter Kassig.

"We prefer our son is written about and remembered for his important work and the love he shared with friends and family, not in the manner the hostage takers would use to manipulate Americans and further their cause," Ed and Paula said in a statement from Indianapolis.

They added that they were "heartbroken" by their son's death and brutal killing, but they are"incredibly proud" of his humanitarian work. They said Kassig "lost his life as a result of his love for the Syrian people and his desire to ease their suffering."

With the beheading of Peter Kassig, the Islamic State has already killed five Westerners it has abducted. American journalists James Foley and Steven Sotloff, as well as British aid workers David Haines and Alan Henning, were brutally beheaded.

In the beheading videos of the two American journalists and two British aid workers, they were shown kneeling in orange jumpsuits while forced to make speeches. Their killer then lifts a knife to their throats. However, the video of the beheading of Peter Kassig released Sunday did not show any decapitation.

The beheading of Peter Kassig also did not show other Western captives, as well as threats of future beheadings. Instead, the footage showed close-ups on some of ISIS members' exposed faces, some of which were foreigners.

The video of the beheading of Peter Kassig reportedly appeared on websites used by the Islamic State in the past. The terrorist group now controls a third of Syria and Iraq.

"This is Peter Edward Kassig, a U.S. citizen ... who fought against the Muslims in Iraq," said a militant in the video of the beheading of Peter Kassig. The black-clad ISIS member appeared to speak with a British accent, which had been distorted to disguise his identity.

In the meantime, the militant with a British accent in previous beheading videos have reportedly been identified by the FBI. However, they have not yet identified the man publicly.

The striking differences in the production of the video of the beheading of Peter Kassig and previous beheadings of Westerners have raised several questions, according to the Independent.

Spanning a total of 16 minutes, the footage of the beheading of Peter Kassig again attempted to show high production techniques, showing the history of the birth of Isis and the group's growth over the years making them what they are today. There is also a narration with English subtitles, as well as a soundtrack.

Despite the slow-motion moments and added sound effects however, there can be no doubting the inhumanity of the beheading of Peter Kassig. At the tail end of the footage, it showed Kassig's head seemingly shot in bad lighting, taken using only one camera.

As of the current moment, it is the task of the US and British intelligence agencies to understand what the new beheading video means.

French terrorism expert Jean-Charles Brisard was amongst individuals supposing that Kassig resisted the militants, or even tried to escape.

"Obviously there was something that happened during the filming", Brisard told The New York Times. "We know that the past executions were filmed from multiple perspectives, so perhaps something happened here that prevented them from doing so."

The footage of the beheading of Peter Kassig reportedly identified the militants' location as being in Dabiq, a town in northern Syria which the terrorist group uses as the title of their English-language propaganda magazine.

"We say to you, Obama: You claim to have withdrawn from Iraq four years ago," the militant said in the video of the beheading of Peter Kassig. "Here you are: You have not withdrawn. Rather, you hid some of your forces behind your proxies."

The U.S. is targeting the Islamic State through airstrikes, whilst also supporting Syrian rebels, Kurdish fighters and the Iraqi military.

The Islamic State group currently has other captives, of whom include British photojournalist John Cantlie, as well as a 26-year-old American woman captured in Syria the previous year while working for aid groups.

The video of the beheading of Peter Kassig appears part of continuous efforts to strike at the U.S., which is leading an aerial campaign against the group. The aerial attacks reportedly began in August in Iraq and have quickly spread to Syria the following month.

The Peter Kassig beheading video came two days after Abu Bakr al-Baghdadi, the group's leader, uploaded a recording to the Internet, according to the Associated Press.

ISIS has its roots in al-Qaida's Iraqi affiliate. However, it had been expelled from the global terror network because of its brutal tactics and since the group refused to obey orders to confine its activities to Iraq. The militants reportedly became even more severe during the bloody civil war in Syria.

They eventually gained strength enough to launch a lightning offensive across Iraq. The current Syrian war started as an uprising against President Bashar Assad. According to activists, the conflict has already resulted in the deaths of more than 200,000 people.

Kassig served in the U.S. Army's 75th Ranger Regiment, a special operations unit. He was deployed to Iraq in 2007. He returned to the Middle East in 2012 and formed a relief group, Special Emergency Response and Assistance serving Syrian refugees.

The beheading of Peter Kassig is amongst the many innocent deaths resulting from ISIS' terrorism. In this case, the death is more of a loss as Kassig, a certified EMT, has been vigilant in humanitarian efforts in the war-stricken country, delivering food and medical supplies, as well as providing trauma care to wounded Syrians before his capture in eastern Syria on Oct. 1, 2013.

To view the ISIS beheading video of Peter Kassig, click here.