The George Zimmerman trial took a shocking turn at the beginning of the third week of the proceedings Monday when the lead detective in the Trayvon Martin case testified that Martin's father said it was not his son’s voice on the 911 call shortly before the 17-year-old was shot and killed.

The testimony bolsters the argument by Zimmerman’s defense that the voice screaming for help was that of Zimmerman, who claims he shot and killed the teen in self-defense.

Det. Chris Serino of the Sanford Police Department testified Monday in Florida Circuit Court that Tracy Martin, Trayvon’s father, initially said that the audible screams on the tape did not come from his son.

Tracy said that the voice “was not his son,” Serino testified. The lead detective in the case said that that answer was a significant development in the investigation that led to murder charges against Zimmerman.

Serino’s testimony came a week after both the mothers of Martin and Zimmerman took the stand. Both mothers said it was their son’s voice on the 911 call that was made just moments before Zimmerman shot and killed Martin.

Zimmerman is facing second-degree murder charges in the death of Martin. The case gained national attention and spurred a debate about racial profiling. Zimmerman is half-white and half-Hispanic, while Martin, who was unarmed, was black.