Authorities in Saudi Arabia beheaded Abdulatif Zapanta, a Filipino national, on Tuesday, after he spent nearly six years on death row seeking a pardon.

The execution was Saudi Arabia's 158th of 2015, the highest total for any year in the country since 1995. More than 70 people executed this year have been foreign nationals like Zapanta, according to Human Rights Watch.

Zapanta, 35, arrived in Saudi Arabia from the Philippines as an overseas laborer in 2008, and worked in the country as a tile layer and contractor. A year later, he killed his Sudanese landlord, Imam Ibrahim, with a hammer in a violent dispute over rent money, according to the Philippine Department of Foreign Affairs.

Zapanta claimed he had acted in self-defense and that Ibrahim had struck first. Regardless, he was convicted for murder in 2010, a crime that automatically yields a death sentence under Saudi Arabia's strict interpretation of Islamic law. Zapanta was also convicted of robbery for taking Ibrahim's wallet and phone, according to Philippine media.

Barcroft Media/Getty Images A large percentage of the people executed in Saudi Arabia are foreign nationals.

He had hoped to escape execution through the payment of diya, or blood money. Saudi Arabia's legal system allows families to accept this compensation in exchange for pardoning a perpetrator when the conviction is classified under the principle of qisas. Adam Coogle, a Middle East researcher at Human Rights Watch, describe s the concept as a sort of eye-for-an-eye punishment.

"The family of the victim can either forgive the perpetrator with nothing in return, demand what's known as diya or blood money, or they can refuse all of those and see the person executed," Coogle said.

In Zapanta's case, Ibrahim's family demanded 4 million Saudi riyal, or a little over a million U.S. dollars. The figure was far more than Zapanta could pay, and his family and the Philippine government began fundraising to save him.

After several extensions on payment deadlines, as well as attempts from the Philippines to secure its citizen's release, Zapanta was ultimately unable to raise the full sum.

A wide variety of crimes can result in the death penalty in Saudi Arabia, ranging from adultery to apostasy and even sorcery. Murder and drug-related offenses, however, make up the vast majority of death sentences. Beheading is the usual means of execution.

Zapanta is the last person to be have been to death in the country in 2015, and one of 88 executed for murder, according to Human Rights Watch. Drug crime-related convictions made up almost all of the rest of the executions, with 63 people killed.

The number of death sentences the Saudi government carried out in 2015 is significantly higher than the figure in 2014, which was at least 90. That number was itself an increase from the roughly 79 who were executed the previous year, according to Amnesty International estimates.

Saudi experts and human rights groups say it's difficult to pinpoint what is causing the increasing numbers of executions.

It's unlikely that the spike can be attributed to King Salman, who ascended to the throne in January, since use of the death penalty first rose in the last months of former King Abdullah's reign. Specifically, the boom seems to have started in the summer of 2014, when authorities beheaded 19 people over the course of just two weeks in August. Many of the people executed in 2015 were also sentenced years ago, meaning that the root causes of the trend are not necessarily recent.

Experts also point to judicial reform and the specialization of the Saudi court system since 2007, which Coogle says may have increased the efficiency with which the government hands out convictions. Another factor may be the general instability in the region in recent years.

Activists and monitors have routinely criticized Saudi Arabia's justice system for flaws and abuses, including draconian punishments and violations of basic legal rights that result in convictions.

Saudi Arabia regularly ranks third -- behind China and Iran -- among nations in terms of annual number of executions. The two other nations in the top five are Iraq and the United States.

Rebecca Falconer contributed reporting.

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