WAIT! How do we know the AUDIO is authentic on the tape??

The speaker is wearing a mask. How do we know that the audio talking about abuse of prisoners wasn't dubbed in??

The video could be up to a month old. With new audio for strategic purposes.

could very well be a false assumption. The victim had not been heard from by his family since April 9th, according to this article:

http://www.pennlive.com/newsflash/pa/index.ssf?/base/news-16/108430077760820.xml

and WilliamPitt posted this translation of what they said:

One of the executioners read a statement: "For the mothers and wives of American soldiers, we tell you that we offered the U.S. administration to exchange this hostage with some of the detainees in Abu Ghraib and they refused. So we tell you that the dignity of the Muslim men and women in Abu Ghraib and others is not redeemed except by blood and souls. You will not receive anything from us but coffins after coffins ... slaughtered in this way." The men then cut Berg’s head off with a knife and held his head up for the camera.

from this thread:
http://www.democraticunderground.com/discuss/duboard.php?az=view_all&address=104x1579249#1579313

From the above translation, there is no mention of torture, it speaks about dignity which makes me think that the beheading happened prior to the publicizing of the torture photos and reports.