Due to the statue of limitations (8 years), his Athens 2004 urine samples (last major competition) can't be retested again (with the new drug testing metods recently discovered)
He did not compete after Athens 2004. But he was not retired in 2005. He was running and doing mileage. El Guerrouj also left it late before deciding to withdraw from the 2005 Worlds because of a virus. He then declared he would take the rest of the year off before racing a farewell season in 2006. And finally...he retired early in 2006.
So for the records,El G is clean...and he never failed a single test.
And the same with another athletes retired from major competitions before 2006 like Kelly Holmes, Noah Ngeny, Daniel Komen, Wilson Kipketer, Paul Tergat, etc.