A U.S. military official in Baghdad confirmed that Fox's remains were picked up by American forces on Thursday evening, although they were not immediately identified. He had no information on the condition of the body.
A police patrol was also on the scene, said Falah al-Mohammedawi, an official with the Interior Ministry, which oversees police. He said Fox was found with his hands tied and gun shots to his head and chest. There were also cuts on his body and bruises on his head, al-Mohammedawi said.
There was no immediate word on the whereabouts of Fox's fellow hostages: Canadians James Loney, 41, and Harmeet Singh Sooden, 32; and Briton Norman Kember, 74. They were last seen in a video dated Feb. 28 that was broadcast Tuesday on Arab television. Fox did not appear in the brief footage.
The previously unknown Swords of Righteousness Brigades claimed responsibility for kidnapping the four workers, who disappeared Nov. 26.
The FBI verified that a body found in Iraq Friday morning was that of Fox, 54, of Clear Brook, Va., spokesman Noel Clay said. He said he had no information on the other three hostages.
Clay said additional forensics will be done in the United States. The U.S. Embassy in Baghdad is investigating, he said.
It is not uncommon for the FBI to get involved in cases involving Americans abducted overseas, but an FBI spokesperson says the bureau has no additional information about this case, CBS Radio reported.
Fox's family has been notified, Clay said, and "our heartfelt condolences go out to them."
"The State Department continues to call for the unconditional release of all other hostages" in Iraq, the spokesman said.
Fox was the one American among four Christian Peacemaker activists kidnapped last year in Iraq.
On Tuesday, Al-Jazeera television aired footage of the three other activists purportedly appealing to their governments to secure their release.
Allan Slater, a Canadian member of Christian Peacemaker Teams, said at the time that he was disturbed not to see Fox.
"We certainly are hopeful when we see three of our friends alive, but also it's very distressing that we didn't see Tom Fox, and I wouldn't want to hide that because I'm sure it's very distressful for Tom's family and friends as well," Slater told The Canadian Press from Baghdad.
The four had not been heard from since a videotape aired by Al-Jazeera on Jan. 28, dated from a week before. A statement reportedly accompanying that tape said the hostages would be killed unless all Iraqi prisoners were released from U.S. and Iraqi prisons. No deadline was set.
Fox, who was a Quaker, was the father of two college-age children, the Washington Post reported. He was an assistant manager at Whole Foods in Springfield, Va., before quitting to join Christian Peacemaker Teams. He had been going to Iraq since September 2004.
Committed to peace, Fox was a former student at the Center for Justice and Peacebuilding at Eastern Mennonite University in Harrisonburg, Va., reported the city's newspaper, the Daily-News Record.
Iraqi and Western security officials repeatedly warned the activists before their abduction that they were taking a grave risk by moving around Baghdad without bodyguards.
Christian Peacemaker Teams had been working in Iraq since October 2002, investigating allegations that U.S. and Iraqi forces abused Iraqi detainees. Its teams host human rights conferences in conflict zones, promoting peaceful solutions.
In the three years since the U.S.-led coalition invaded Iraq, insurgents have kidnapped at least 250 foreigners and killed at least 40 of them.
In one of the most high-profile cases, Jill Carroll, a freelance writer for The Christian Science Monitor, was kidnapped Jan. 7 in Baghdad. Three videotapes of Carroll delivered by her kidnappers to Arab satellite television stations identified the group holding her as the Revenge Brigades.
Carroll's kidnappers have publicly demanded the release of all female detainees in Iraq. The Monitor launched a campaign on Iraqi television stations Wednesday asking Iraqis, in Arabic, to "Please help with the release of journalist Jill Carroll."
The list of those kidnapped and killed in Iraq includes Margaret Hassan, the director of CARE international in Iraq and a citizen of Britain, Ireland and Iraq; Ronald Schulz, an industrial electrician from Anchorage, Alaska; Nicholas Berg, a businessman from West Chester, Pa.; Jack Hensley, a civil engineer from Marietta, Ga.; and Eugene "Jack" Armstrong, formerly of Hillsdale, Mich.