The news comes as violence continued in Mexico after at least 11 people, including six children, were killed in three drive-by shootings in Mexico's southeastern
Tabasco state, local authorities said on Sunday.
The dead were mostly relatives of a Mexican state police officer, officials said.
Ramirez was appointed as Mexico's top anti-drug prosecutor by Felipe Calderon, Mexico's president, in 2006.
Two other anti-drug officers were imprisoned in 2008 for accepting bribes of up to $500,000 from the Beltran Leyva gang, which had recently split from Sinaloa cartel.
Calderon's two-year-old crackdown on drug cartels has sparked brutal violence as cartels battle for turf and power, with around 6,000 people dying in the fighting last year, many of them civilians.