Al Jazerra is airing the video they said.
I think they are saying that Al Jazeera HAS the video, but has not shown it. Al-J seems to have realized that all these executions of Westerners are not endearing their beloved "militants" to the west.
From what I am reading it does appear that Maupin has been killed. The Army has seen a video of a blindfolded man who "looks like him" being shot in the head in a darkened room. No confirmation, but...doesn't look good.
Prayers for his family in their darkest hours.