Why was one US hostage in Syria killed, and another freed?

American freelance writer Peter Theo Curtis was released Sunday by an Al Qaeda affiliate in Syria, just days after James Foley was executed by another Islamist terror group.

No one knows for sure why American freelance writer Peter Theo Curtis was released Sunday by an Al Qaeda affiliate in Syria, just days after another American journalist held captive in Syria, James Foley, was brutally executed on camera by another Islamist terror group.

But two factors may help explain the excruciatingly divergent outcomes in the cases.

One is the differences in the groups that were holding the two men.

The other is the fact that the government of Qatar, a country that is both a partner of the United States in the Middle East and a contact for some radical Sunni Muslim organizations in the region, was involved in negotiations for Mr. Curtis’s release.

Mr. Foley was held by the Islamic State (IS) – which since June has advanced from Syria into northern Iraq and which the US is now bombing on the Iraqi side of the border. Curtis was held by Jabhat al-Nusra, or Nusra Front, a Syrian group fighting the forces of Syrian President Bashar al-Assad (whom the US also opposes) and linked to Al Qaeda.

The two groups may seem like two sides of the same coin. But there are key differences in tactics, objectives, and regional associations separating the two, regional and counterterrorism experts say.

IS, also known as ISIS, the group that held Foley for nearly two years, started out a decade ago as Al Qaeda in Iraq and distinguished itself by its over-the-top cruelty and willingness to attack civilians in an effort to foment sectarian war. The group was eventually excommunicated from Al Qaeda for what AQ leader Ayman al-Zawahiri deemed extreme violence – in particular against other Muslims – that he said was counterproductive. The group has also declared an Islamic “caliphate” spanning Syria and northern Iraq, a move that former AQ leader Osama bin Laden had opposed as premature.

Nusra Front split off from IS earlier this year, after the AQ leadership disavowed IS. In the view of some, Nusra Front – more focused on the battle against Mr. Assad – may have decided to release Curtis as a way of distinguishing itself from IS, including in the eyes of other rebel factions in Syria’s civil war.

Nusra Front is also locked in conflict with IS on the battlefront. According to reports from Syria, Nusra Front forces on Sunday forced IS fighters from a base they’d established in Homs in northern Syria.

Nusra Front has maintained contacts with Qatar, which has been involved in negotiating with the group on other hostage releases. Earlier this year, Qatar paid the ransom that led to the release of a group of nuns and other women captured by the group in Syria.

In a statement Sunday, the Curtis family said it had been told by Qatari officials that no ransom was paid for Curtis and that they had helped negotiate his release “on a humanitarian basis.”

By mediating Curtis’s release, Qatar may have been looking to bolster its standing with the US, which maintains a military base in the Persian Gulf country.

US officials say they do not see a link between Foley’s murder and Curtis’s release just a few days later. Obama administration officials did appear to try to soften the painful juxtaposition of one American hostage’s release with another’s brutal execution.

Samantha Power, the US ambassador to the United Nations, said in a statement that both Foley and Curtis “traveled to Syria to shed light on the unspeakable horrors being committed against innocents – only to become victims of brutal forces unleashed and abetted by the conflict.”

Ambassador Power was involved in connecting the Curtis family with the government of Qatar through the Qatari ambassador to the UN. On Sunday, Curtis was released to UN peacekeepers in the disputed Golan Heights zone between Syria and Israel.

Despite official US doubts about Curtis’s release coming in response to Foley’s murder, terrorism experts note that terror groups are vying for varying audiences and, as George Washington University terrorism expert Jerrold Post says, are largely engaged in “psychological warfare.”

Groups like IS and Nusra Front are waging war to varying degrees against each other. In that sense, some say, it is impossible to dismiss the rapid succession of outcomes in the two hostage cases as mere coincidence.