A neighbor of George Zimmerman who had perhaps the best view of the struggle between the neighborhood watch volunteer and Trayvon Martin testified at Zimmerman's murder trial Friday that it appeared the unarmed teen was straddling Zimmerman during their confrontation.

However, Jonathan Good said he did not see anyone's head being slammed into the concrete sidewalk, which Zimmerman has said Martin did to him. Good initially testified that it appeared "there were strikes being thrown, punches being thrown," but during detailed questioning he said he saw only "downward" arm movements being made.

Zimmerman has claimed that he fatally shot 17-year-old Martin last year in self-defense as the Miami-area teen was banging his head into the concrete sidewalk behind the townhomes in a gated community.

But under prosecution questioning, Jonathan Good said he never saw anyone being attacked that way during the fight between Zimmerman and Martin.

"I couldn't see that," Good said moments later while being cross-examined.

Good, the second person to take the witness stand Friday, said he heard a noise behind his townhome in February 2012, and he saw what looked like a tussle when he stepped out onto his patio to see what was happening.

He said he yelled, "What's going on? Stop it."

Good testified he saw a person in black clothing on top of another person with "white or red" clothing. He said he couldn't see faces but it looked like the person on the bottom had lighter skin. Martin was black and was wearing a dark hoodie. Zimmerman identifies as Hispanic and was wearing a red jacket.

"It looked like there were strikes being thrown, punches being thrown," Good said.

Later, under cross-examination, he said that it looked like the person on top was straddling the person on bottom in a mixed-martial arts move known as "ground and pound." When defense attorney Mark O'Mara asked him if the person on top was Martin, Good said, "Correct, that's what it looked like."

Good also said the person on the bottom yelled for help.

During cross-examination, O'Mara got on his knees to recreate the fighting as he asked Good to walk him through it.

Good was in the middle of dialing 911 inside his townhome when he heard a gunshot, he said.

Zimmerman, 29, could get life in prison if convicted of second-degree murder. Zimmerman followed Martin in his truck and called a police dispatch number before he and the teen got into a fight.

Zimmerman has denied the confrontation had anything to do with race, as Martin's family and their supporters have claimed.

A second former neighbor of Zimmerman testified after Good. Jonathan Manalo, whose wife had testified earlier in the week, was the first neighbor to step outside and see what happened with his flashlight after he heard a gunshot. He took cellphone photos of a bloodied Zimmerman and Martin's body, and those photos were shown to jurors on Friday. Manalo also described Martin's hands as being under his body.

Manalo said Zimmerman didn't appear shocked and acted calmly. After police officers arrived and handcuffed Zimmerman, the neighborhood watch volunteer asked Manalo to call his wife and tell her what happened.

Manalo started to tell Zimmerman's wife that her husband had been involved in a shooting and was being questioned by police when "he cut me off and said, `Just tell her I shot someone,'" Manalo said.

Under cross-examination, Manalo said when he asked Zimmerman what happened, the neighborhood watch volunteer told him, "I was defending myself and I shot him."

"From what you could tell at that moment, that seemed completely true?" asked defense attorney Don West.

"Yes," Manalo said.

Before Good testified, a worker at a video surveillance company that maintains cameras at the townhome community took the witness stand. A prosecutor played two videos from surveillance cameras; one showed what looks like a person walking past a window at the complex's clubhouse, and another showed what looks like a light by the complex's mailboxes.

Greg McKinney said the digital clock on the video is off by 18 minutes, a point O'Mara hammered home by getting McKinney to concede the timing difference was inexact and could be more than 18 minutes.

Jurors already have been shown some of the state's biggest pieces of evidence, including the 911 call featuring cries for help prosecutors believe came from Martin.

On Thursday, a friend of Martin who had been on the phone with him when he was shot testified about what she heard during his confrontation with Zimmerman.

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Follow Kyle Hightower on Twitter at http://twitter.com/KHightower

Follow Mike Schneider on Twitter at http://twitter.com/MikeSchneiderAP