twelve felony cases , 19 criminal misdemeanor cases and one juvenile case involving one or more of the officers were dismissed .
officers exchanged ` inexcusable ' racist text messages , police chief said .
messages referred to ` killing n ****** ' ; one said , ` i 'd have that noose ready '
alvarez also created video featuring obama sporting gold-capped teeth .
other clips included pictures of attacks on minorities and use of n-word .
james wells , jason holding and christopher sousa were fired in march .
colleague alex alvarez , 22 , resigned in late january during investigation .