 Kirk Acevedo (qv) was absent from most of the first half of the  fourth season because he was working on  _"Band of Brothers" (2001) (mini)_ (qv). On the show, it was  explained that Miguel Alvarez had escaped. Acevedo returned for the  second half of the fourth season. But shortly after production began  on the second half, he landed a recurring role on  _"Third Watch" (1999)_ (qv) and had to leave "Oz" again. This time,  it was explained that Alvarez had been put in solitary confinement.  In some episodes, archive footage of Acevedo from past episodes was  reused.