Why The USA Didn't Want al-Zarqawi

First we heard that the US turned down a Taleban deal to hand over bin Laden, now we hear they turned down an Iranian offer of al-Zarqawi. Why?

Juan Cole has an educated guess:

"Iran is reported to have Abu Musab al-Zarqawi in custody in summer of 2003, and to be entirely willing to hand him over to the US in return for some high-ranking MEK terrorists. But first the neocon network... intervenes to stop the trade... Then, mysteriously, everything that goes wrong in Iraq from about January of 2004 begins being blamed on Zarqawi (is it alleged that Iran let him go, to deliberately disrupt Iraq by blowing up Shiites? More likely, when Iran won't accommodate the Neocons because of the latters' ties to MEK, the neocons decide to smear Iran as 'harboring' terrorists and 'sending' them to Iraq. They know this path might even lead to a US war on Iran, which is what they want. That is one reason they did not want the prisoner exchange to succeed). "