SANFORD, Fla. (TheBlaze/AP) — The lead investigator probing Trayvon Martin’s death testified on Monday that his father had answered “no” when the detective asked if the screams belonged to his son. Officer Chris Serino played the 911 call for Tracy Martin in the days immediately following Martin’s death in February 2012.

“He looked away and under his breath he said ‘no’,” Serino said of Tracy Martin.

Officer Doris Singleton backed up Serino’s account.

Detective: Trayvon Martins Dad Answered No When Asked if Screams on 911 Call Belonged to His Son

SANFORD, FL – JULY 8: Sanford police officer Chris Serino testifies as a defense witness in the George Zimmerman trial in Seminole circuit court July 8, 2013 in Sanford, Florida. Credit: Getty Images

Detective: Trayvon Martins Dad Answered No When Asked if Screams on 911 Call Belonged to His Son

SANFORD, FL – JULY 01: Sanford police officer Doris Singleton holds up a copy of George Zimmerman’s written statement from the night of the shooting, during Zimmerman’s murder trial in Seminole circuit court July 1, 2013 in Sanford, Florida. Credit: Getty Images

However, Tracy Martin testified that he never denied it was his son’s voice screaming for help on a 911 call, contradicting police officers’ earlier testimony at George Zimmerman’s second-degree murder trial.

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.

Detective: Trayvon Martins Dad Answered No When Asked if Screams on 911 Call Belonged to His Son

SANFORD, FL – JULY 8: The Father of Trayvon Martin, Tracy Martin, testifies as a defense witness in George Zimmerman trial in Seminole circuit court, July 8, 2013 in Sanford, Florida. Credit: Getty Images

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.

During cross examination of Serino, prosecutor Bernie de la Rionda suggested that Tracy Martin may have been in denial about his son’s death and uttered, ‘no.”

“It could be perceived as denial,” Serino said.

The investigator’s testimony was just the latest effort to determine who was crying for help on the 911 calls. A series of Zimmerman’s friends on Monday testified that the screams on the recording were their friend, and the 911 call was played multiple times in the courtroom.

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