This is all according to Islamic law. Here is a salient passage on this issue from a Shafi’i manual of Islamic law:

When an adult male is taken captive, the caliph considers the interests … (of Islam and the Muslims) and decides between the prisoner’s death , slavery, release without paying anything, or ransoming himself in exchange for money or for a Muslim captive held by the enemy. (Reliance of the Traveller o9.14)

A revered Islamic jurist, Al-Mawardi, agrees with Reliance of the Traveller:

As for the captives, the amir has the choice of taking the most beneficial action of four possibilities: the first, to put them to death by cutting their necks; the second, to enslave them and apply the laws of slavery regarding their sale or manumission; the third, to ransom them in exchange for goods or prisoners; and fourth, to show favor to them and pardon them. (Al-Ahkam As-Sultaniyyah (The Laws of Islamic Governance), 4.5)

“Kirk Woodman, Canadian kidnapped in Burkina Faso, found dead,” CBC News, January 17, 2019 (thanks to The Religion of Peace):

A Canadian kidnapped in Burkina Faso has been found dead, says his family, two days after he was abducted.

Kirk Woodman, originally from Halifax, was abducted Tuesday night by a dozen gunmen at a mining site owned by Vancouver-based Progress Minerals in Tiabongou, near the border with Niger, in an area the government says is under growing threat from armed jihadists….

A spokesperson for the Burkina Faso Security Ministry told Radio-Canada that Woodman had been shot and his body was found Wednesday night, 100 kilometres from the site where he worked….

Alpha Barry, Burkina Faso’s minister of foreign affairs and co-operation, referred to Woodman’s death as an “assassination.”

“The government of Burkina condemns with the utmost energy this cowardly assassination and reassures that an investigation is opened and all the measures will be taken to find and punish the guilty,” he said in a statement in French posted to Facebook on Thursday….

David Duncan, a veteran exploration geologist based in Windsor, N.S., said he worked with Woodman on projects in the province and overseas for more than four decades.

In an interview Wednesday, he described Woodman as a talented geologist — part of a wider community of Nova Scotia-trained geologists who helped find mines around the globe. He had the ability to tell whether a good prospect could become a producing mine, said Duncan.

Duncan and Woodman worked for Etruscan Resources of Halifax on some of the first gold mines in Niger and then in Burkina Faso — as part of a close-knit group of Canadian geologists pioneering the development of mines in western Africa.

He said working as an exploration geologist in western Africa always had its dangers, ranging from the risk of traffic accidents to contracting diseases such as malaria, but Duncan said in recent years that the risk increased with the rise of Islamic militancy.

“It’s a terrible thing, a terrible thing. We understood since the Canadian diplomat Robert Fowler was kidnapped in Niger that part of the world had changed … with the introduction of Islamic fundamentalists into that part of the world,” he said.

“It’s gotten to be a much harder place… We were never worried about being kidnapped. Today, it’s a different world.”

He’s the second Canadian to go missing in the country in recent weeks, Burkina Faso Security Minister Clément Sawadogo said.

Quebec resident Edith Blais, 34, and her Italian travel companion, Luca Tacchetto, 30, were last heard from in the western city of Bobo-Dioulasso on Dec. 15….