The judge in the murder trial of Florida neighborhood watchman George Zimmerman has ruled that a toxicology report on 17-year-old Trayvon Martin showing that Martin used marijuana can be shown to the jury.

The judge in the case had previously ruled that the toxicology report would be not be admitted, but a defense attorney for Zimmerman argued that a medical examiner testified the marijuana in Martin's system could have had an effect on his behavior, and so the evidence should be allowed in,

A very big blow to state: Judge: I'm gonna let jurors hear that #Trayvon had marijuana in his system. #Zimmerman — Rene Stutzman (@renestutzman) July 8, 2013

JUST IN: Judge will allow toxicology report into #ZimmermanTrial that says Trayvon had very small amount of THC in his bloodstream. — Michael Skolnik (@MichaelSkolnik) July 8, 2013

Judge reverses pre-trial ruling, says Zimmerman defense can tell jury that Trayvon Martin had marijuana in body when he was shot. — Matthew Keys (@MatthewKeysLive) July 8, 2013

Martin had

, the active ingredient in marijuana, in his system at the time of his death.

Zimmerman shot and killed Martin on Feb. 26, 2012, in a Sanford, Florida neighborhood. Zimmerman claims he shot Martin in self-defense, while the state contends it was second-degree murder.

Martin's father testified earlier Monday that he never denied it was his son's voice screaming for help on a 911 call, contradicting police officers' earlier testimony.

Tracy Martin said that he merely told officers he couldn't tell if it was his son after his first time listening to the call.

"I never said that wasn't my son's voice," said Tracy Martin, who added that he concluded it was his son after listening to the call as many as 20 times.

Tracy Martin's testimony came after the lead investigator probing Martin's death testified that the father had answered "no" when the detective asked if the screams belonged to Trayvon Martin. Officer Chris Serino played the 911 call for Tracy Martin in the days immediately following Trayvon Martin's death.

"He looked away and under his breath he said 'no'," Serino said of Tracy Martin.

Officer Doris Singleton backed up Serino's account.

Convincing the jury of whose voice is on the tape is important to both sides because it would help jurors decide who was the aggressor in the confrontation that left Martin dead. Relatives of Martin's and George Zimmerman's have offered conflicting opinions about who is heard screaming.

The trial continues Tuesday.

The Associated Press contributed to this report.