CNN reports that Zarqawi was in the hands of Iraqi Security Forces last year, who let him go:

BAGHDAD, Iraq (CNN) — Iraqi security forces caught the most wanted man in the country last year, but released him because they didn’t know who he was, the Iraqi deputy minister of interior said Thursday.

Hussain Kamal confirmed that Abu Musab al-Zarqawi — the al Qaeda in Iraq leader who has a $25 million bounty on his head — was in custody at some point last year, but he wouldn’t provide further details.