"My money would be on al Zarqawi:" http://abcnews.go.com/sections/GMA/Investigation/nick_berg_clues_040513-1.html
There is one problem. Al-Zarquawi is believed to be dead since April 2003, as AsiaTimes wrote 2 months ago:
"...For its part, the leadership of the Allahu Akbar Mujahideen - which includes plenty of Sunni resistance groups - circulated a leaflet in Fallujah dismissing the purported al-Zarqawi letter found on a computer disk by the US stating plans for provoking a sectarian war between Sunnis and Shi'ites.
The letter on the disk is described as "the fabricated al-Zarqawi memo", used by the Americans "to back up their theory of a civil war" in Iraq. In fact, the Mujahideen claim that Zarqawi was killed in the Sulaimaniyah Mountains in northeastern Kurdistan "during the American bombing" of Ansar al-Islam positions in late April 2003. Zarqawi, they claim, could not evade the bombing because of his artificial leg..."
The Circumstances of Berg's whereabouts since March 24th are unexplained either. According to Chicago Tribune (KRT) , "Iraqi security forces arrested Berg in late March at a checkpoint near Mosul, according to U.S. officials in Washington familiar with the case. Berg's parents said they did not hear from their son between March 24 and roughly April 8, according to court papers they filed in Pennsylvania last month..."
http://inn.globalfreepress.com/modules/news/article.php?storyid=185