From this source:
The Army didn't say how or where in Iraq his son's remains were discovered, only that the identification was made with DNA testing, Maupin said. A shirt similar to the one his son was wearing at the time of his disappearance was also found.
The Army was continuing its investigation, Maupin said.
Lt. Lee Packnett, an Army public affairs officer in Washington, said an official statement about the identification would be released Monday.
Matt Maupin was a 20-year-old private first class when he was captured April 9, 2004, after his fuel convoy, part of the Bartonville, Ill.-based 724th Transportation Company, was ambushed west of Baghdad.
A week later, the Arab television network Al-Jazeera aired a videotape showing a stunned-looking Maupin wearing camouflage and a floppy desert hat, sitting on the floor surrounded by five masked men holding automatic rifles.
That June, Al-Jazeera aired another tape purporting to show a U.S. soldier being shot. But the dark and grainy tape showed only the back of the victim's head and not the execution.
I await the Army's statement, and am thankful to see that Matt Maupin can now be laid to proper rest.