A U.S. rescue operation earlier this summer failed to free American journalist James Foley and others being held by ISIS in Syria, a U.S. official told CNN on Wednesday.
The Pentagon confirmed a rescue attempt, but did not say whether Foley was among those U.S. officials were hoping to free.
"Unfortunately, the mission was not successful because the hostages were not present at the targeted location," Pentagon spokesman Rear Adm. John Kirby said.
A U.S. official, speaking on condition of anonymity, told CNN the mission was to rescue Foley and other American hostages being held at an undisclosed location.
The news came the same day that it was revealed Foley's family was contacted a week ago by his captors, who said in a rage-filled email the journalist would be executed.
A video released by ISIS on Tuesday showed Foley being beheaded and warned that a second American would be killed if the United States did not end its military operations in Iraq.
"The message was vitriolic and filled with rage against the United States. It was deadly serious," said Philip Balboni, CEO of the online publication GlobalPost.
"Obviously, we hoped and prayed that that would not be the case ... Sadly, they showed no mercy."
In the video, which CNN is not showing, Foley is seen on his knees and a man cloaked in black stands behind him.
Foley is then executed.
The video of his killing also shows another U.S. journalist, believed to be Steven Sotloff. The militant in the video, who speaks English with what sounds like a British accent, says the other American's life hangs in the balance, depending on what President Barack Obama does next in Iraq.
'Jim was innocent'
Foley, a freelance journalist, was on assignment for GlobalPost when he disappeared on November 22, 2012, in northwest Syria, near the border with Turkey.
ISIS, the militant group seeking an Islamic caliphate stretching from Iraq into Syria, has claimed credit and U.S. intelligence said that the video is real.
"Jim Foley was an incredibly brave journalist and an incredibly brave man, right to the horrible end of his life. We are devastated by his loss," Balboni told reporters. "Jim represented the best of the profession of journalism and what it can be and what it should be in its finest hour."
In the video posted on YouTube, Foley reads a message, presumably scripted by his captors, that his "real killer'' is America.
"I wish I had more time. I wish I could have the hope for freedom to see my family once again," he can be heard saying in the video.
His parents, flanked by one of Foley's brothers, talked to reporters Wednesday.
"Jim was innocent and they knew it," Diane Foley said. "They knew that Jim was just a symbol of our country."
His father, John, broke down several times.
"We beg compassion and mercy" for those believed to be holding the other American journalist shown in the video. Sotloff, a contributor to Time and Foreign Policy magazines, was kidnapped at the Syria-Turkey border in 2013.
"They never hurt anybody," John Foley said. "They were trying to help. There is no reason for their slaughter."
Foley had previously been taken captive in Libya. He was detained there in April 2011 along with three other reporters and released six weeks later.
Afterward, he said that what saddened him most was knowing that he was causing his family to worry.
His parents talked about asking him why he wanted to return to conflict zones.
"Why do firemen keep going back to blazing homes?" John Foley told reporters. "This was his passion. He was not crazy. He was motivated by what he thought was doing the right thing...that gave him energy to continue despite the risk."
His mother remembers him telling her, 'Mom, I found my passion, I found my vocation.'"
Foley, 40, grew up in New Hampshire and graduated from Northwestern University's Medill School of Journalism in 2008.
Like some other young journalists working after the September 11 terror attacks, Foley was drawn to Iraq, Afghanistan and other areas of conflict.
Friends described Foley as fair, curious and impressively even-tempered.
"Everybody, everywhere, takes a liking to Jim as soon as they meet him," journalist Clare Morgana Gillis wrote in a blog post about him in May 2013, six months after he disappeared in Syria.
"Men like him for his good humor and tendency to address everyone as 'bro' or 'homie' or 'dude' after the first handshake. Women like him for his broad smile, broad shoulders, and because, well, women just like him."
Searching for clues
ISIS has carried out executions, including beheadings and other horrific acts against people in Iraq as the group led a quick and intense advance in the country. ISIS -- which refers to itself as the Islamic State -- has videotaped executions and posted them online.
U.S. and British counterterrorism analysts are examining every frame and piece of audio of the video for clues about where it took place and who the executioner is, U.S. officials told CNN. The voice in the video seems to have a British accent so they're trying to match any individuals known to the British government who may have gone to Syria to fight in that nation's civil war.
The analysts are looking at clothing, climate, terrain, language and wording and whether there are any National Security Agency or UK phone intercepts matching the voice, officials said Wednesday.
"No matter how long it takes, we put resources behind finding and bringing to justice people who kill Americans," said U.S. State Department spokeswoman Marie Harf.
Harf said that she has not watched the video and doesn't intend to.
French journalist held with Foley shocked
French journalist Nicolas Henin had been held with Foley in northern Syria, but Henin was released in April, he told France Info radio.
The French Foreign Ministry confirmed that Henin was taken hostage June 22, 2013, while on assignment for Le Point magazine and the TV channel Arte.
Henin said he has never before spoken about his experience because he didn't want to jeopardize Foley or other captives' safety.
The French journalist collapsed when he heard about Foley's death, he said.
Henin said he was held hostage for 10 months in Syria, seven of those months with Foley, and described the American journalist as a great friend. Foley was someone with "enormous generosity" who has "extraordinary human qualities..." Henin said. "He was always available to help others, to bring up our spirits."
Hostages were held in groups. At one point, he shared a cell with Foley.
Foley "was in a difficult state," said Henin. "He already suffered a lot during his first months (of captivity) and thankfully we shared a phase (in our detention) that was less difficult."
Foley told Henin he had been initially kidnapped by a group of jihadists who were fighting in Syria.
At that time, ISIS did not exist and the group that was holding them eventually became part of the ISIS movement, the French journalist said.
Henin said that Foley told him he was never held by the Syrian regime or any group associated with the Syrian regime.
Henin and a French photojournalist, who was captured at the same time were freed along with two other French journalists in April.
The Committee to Protect Journalists estimates there are about 20 journalists missing in Syria, many of them held by ISIS.
Among them is American Austin Tice, a freelance journalist who was contributing articles to The Washington Post. Tice disappeared in Syria in August 2012. There has been no word of from him since his abduction.
The CEO of the Associated Press said in a statement that the news service is "outraged" by Foley's killing and "condemns the taking of any journalist's life."
"We believe those who kill journalists or hold them hostage should be brought to justice," Gary Pruitt said. "Further, we believe the assassination of a journalist in wartime should be considered an international crime of war. The murder of a journalist with impunity is a threat to a free press and democracy around the world."
Previous brutal killings of Americans
Foley's killing recalled the murder of Daniel Pearl, The Wall Street Journal correspondent who was kidnapped while reporting in Pakistan in January 2002. His killing was captured on video and posted on line by al Qaeda.
Pearl's mother, Ruth Pearl, responded to Foley's death with a tweet issued from the Daniel Pearl Foundation account that reads, "Our hearts go out to the family of journalist James Foley. We know the horror they are going through."
Foley's death also harkened to the videotaped beheadings of Americans Nicholas Berg, Eugene Armstrong and Jack Hensley carried out by al Qaeda during the height of the Iraq War.
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