Over one year ago, Trayvon Martin was shot and killed while walking from a convenience store to his home in his Florida neighborhood. The shooter, George Zimmerman, claims that he shot Martin in self-defense, but he is now on trial for the 17-year-old’s murder.

This week, a pre-trial hearing for Zimmerman’s trial turned to the topic of the shouts heard on a 911 call recorded at the time of the incident. Zimmerman had called a non-emergency police number at the time of the incident. Martin was also on the phone, with a female friend who has stated she heard Martin say, “Why are you following me?” shortly before his death.

According to an Associated Press report on the trial, the prosecution has hired audio experts to determine whether the shouts heard on the call recording were those of Zimmerman or Martin. Of the two experts cited in the story, one found that the shouts were Martins and the other found they were a mix of both Zimmerman and Martin. In a court filing, Zimmerman’s lawyer has stated that he believes the audio analysis could prejudice jurors, and should not be allowed at the trial.

Since he was charged with Martin’s murder, Zimmerman has been in hiding and using various schemes to pay for his legal representation.