Dr Alvarez, a gynaecologist, was freed when the judge found there was not enough evidence to convict him on charges that he injected Enrique Camarena with drugs to keep him alive while he was being tortured and interrogated by Mexican drug lords.
A jury in Los Angeles has convicted Dr Alvarez's co-defendant, Ruben Zuno Arce, a brother-in-law of a former Mexican president. He was found guilty of conspiring to kidnap and murder Camarena, and faces possible life imprisonment. He is the seventh person convicted in US courts over the Camarena murder, in 1985. A businessman, was found guilty in 1990, but the verdict was later overruled.