- Ed and Paula Kassig plead for ISIS to release their son
- Abdul-Rahman Kassig served as a U.S. Army Ranger and went to Syria as an aid worker
- He was featured at the end of an ISIS video showing the beheading of Alan Henning
- Henning was a "local and national hero," a joint statement from 200 mosques says
Another gruesome video. Another beheading of a Western captive by ISIS. And another family warned that its loved one may be next.
For Alan Henning's family, the nightmare has turned into reality. Now Abdul-Rahman Kassig's family is hoping for a miracle.
Both Henning and Kassig risked their lives to help strangers besieged by the Syrian civil war.
Over the weekend, hundreds of people attended a service in Manchester, England, to remember Henning. And Sunday night, Kassig's parents issued another plea for their son.
Here are the stories of the aid workers snatched by militants bent on using them as political pawns:
Henning: A 'national hero'
Not even the calls of 200 mosques in Britain were enough to stop radical militants from decapitating Henning, a 47-year-old taxi driver from near Manchester.
"Alan Henning was our local and national hero," a joint statement from the mosques said. "We will remember him as a tireless and selfless volunteer aid worker whose only concern was to help people in need."
The mosques also slammed the terror group who took him.
"The killing of Alan Henning was a cowardly and criminal act of appalling brutality by a group who do not represent Islam at all and in fact are an insult to the Islamic faith," their statement said.
Henning joined a group of volunteers who traveled to Syria in December 2013 to deliver food, water and medical supplies to people afflicted by the country's devastating civil war.
He was abducted by masked gunmen the day after Christmas, other people in the aid convoy said.
His wife, Barbara, pleaded for her husband's release, but to no avail.
ISIS released the video of Henning's decapitation on Friday. It said the killing was a response to the UK joining the U.S.-led bombing campaign against the group in Iraq and Syria.
Some of Henning's fellow aid workers believe the British Parliament's decision to authorize bombing ISIS in Iraq may have triggered their friend's slaughter.
"By joining the U.S. airstrikes, we handed Alan, and many other Western hostages, a death sentence," aid worker Dr. Shameela Islam-Zulfiqar said.
But British Prime Minister David Cameron said the "abhorrent" killing of Henning means allies must continue trying to "do everything we can to defeat this organization."
And as it did in the beheading videos of American freelance journalists James Foley and Steven Sotloff and British aid worker David Haines, ISIS threatened to decapitate another Westerner. It showed American aid worker Abdul-Rahman Kassig and said he would be next.
Kassig: 'I am an idealist'
Kassig, 26, had already finished a tour in the Middle East as a U.S. Army Ranger stationed in Iraq. But he felt compelled to go back to the region to help Syrians caught in a bloody conflict that has killed roughly 200,000 people.
Kassig's given name is Peter, but CNN is honoring his parents' request to refer to him by his Muslim name.
He expressed his fear in captivity in a letter sent to his parents in June.
"I am obviously pretty scared to die, but the hardest part is not knowing, wondering, hoping, and wondering if I should even hope at all," Kassig wrote.
A year before he was captured by ISIS in 2013, Kassig spoke with CNN's Arwa Damon about his need to help.
"The way I saw it, I didn't have a choice. This is what I was put here to do," Kassig said in 2012.
He then founded Special Emergency Response and Assistance, a nongovernmental organization aiding Syrians fleeing the civil war there.
"I am not a doctor. I am not a nurse," he said. "But I am a guy who can clean up bandages, help clean up patients, swap out bandages, help run IVs, make people's quality of life a little bit better. This is something for me that has meaning, that has purpose."
His journey toward converting to Islam began before his capture, his family said.
Kassig's family released a YouTube video Saturday begging the militants to release him.
"We implore his captors to show mercy and use their power to let our son go," his father, Ed Kassig, said.
"We are so very proud of you and the work you have done to bring humanitarian aid to the Syrian people," his mother, Paula, added in the video.
Kassig said going halfway across the world to help strangers wasn't a hard decision.
"I guess I am just a hopeless romantic, and I am an idealist, and I believe in hopeless causes," he told Damon in 2012.
Now, his loved ones hope that pleading for his release isn't a lost cause.