A witness called by the prosecution, Zimmerman's neighbor Selene Bahadoor, said she heard noises and saw two people standing as she looked through a sliding glass door at her home. She could not identify them but described what she saw as "figures and arms flailing."
She then heard a gunshot, she said, and saw a "body in the grass... I remember it lying face down."
Also testifying Tuesday was Sanford Police Sgt. Anthony Raimondo, one of the first officers to arrive after the shooting.
He said he attempted to perform CPR on Martin.
"I attempted to get his pulse. I breathed for Mr. Martin. I tried to, sir," Raimondo said.
As jurors were shown photos of Martin's body, his father, Jesse Martin, left the courtroom. One photo was a close-up of the bullet wound in Martin's chest, the Orlando (Fla.) Sentinel reported.
Diana Smith, a crime scene technician for the Sanford police, explained a diagram of the shooting scene and displayed collected evidence, including items Martin was carrying, the newspaper said.
Wendy Dorival of the Sanford Police Department, overseer of the Neighborhood Watch program Zimmerman coordinated, told jurors Tuesday volunteers are trained not to follow suspicious people because "that's the job of law enforcement."
Zimmerman has pleaded not guilty to second-degree murder in Martin's February 2012 death.