- Zimmerman's brother says his brother acted in self defense
- Brother says he wants to correct 'mythology,' untruths about the case
- "This is a tragedy," Zimmerman's brother says
- Martin's family and some experts say the video suggests Zimmerman was not badly hurt
Sanford, Florida (CNN) -- George Zimmerman's brother said medical records will prove that his brother was attacked and his nose was broken by Trayvon Martin before he fatally shot the teen.
Robert Zimmerman Jr. spoke to CNN's Piers Morgan Thursday night saying he wanted to correct some of the "mythology" and untruths that have been spread about the controversial shooting.
"We're confident the medical records are going to explain all of George's medical history," Zimmerman Jr. said. "His nose looks swollen in that video. I'm his brother."
George Zimmerman, a neighborhood watch volunteer, said he shot Martin in self defense after the teen attacked him last month. Martin, who was walking through the gated community back to the house of his father's fiancee, was wearing a hoodie in the rain and carrying Skittles candy and a can of iced tea he had purchased from a nearby convenience store.
Trayvon Martin witness breaks silence 
How shooting witness impacts Martin case 
'George didn't chase anyone' 
Breaking down the Trayvon police report Authorities have said Zimmerman has not been charged because there are no grounds to disprove his account that he acted in self defense. Critics say Zimmerman, who is Hispanic, racially profiled Martin, who was black.
The shooting of Martin, an unarmed 17-year old, has sparked an intense national debate about race, birthed protests and was addressed by President Barack Obama who called the incident a "tragedy."
Robert Zimmerman Jr. also called the shooting a tragedy but warned that some of the responses have not been healthy.
"This is a tragedy. Her son was lost," he said trying to send a message to Martin's mother. "I feel very badly about that and I want, in the end, not for her son's memory to be seen as how we degraded our system and turned it into mob rule and went into a hate speech. Ultimately, we all wish that this was a different situation."
George Zimmerman has told police he shot Martin in self defense on February 26 in a gated community in Sanford, Florida.
Zimmerman's father said on Wednesday that Martin threatened to kill Zimmerman, broke his nose and beat him so badly that Zimmerman was forced to shoot the teen. Robert Zimmerman Jr., on Thursday, told the same story.
"You return force with force when somebody assaults you. George was out of breath, he was barely conscious," the brother said. "There would have been George dead if he had not acted decisively and instantaneously in that moment when he was being disarmed."
Martin's family and legal experts have questioned the Zimmerman's family version after the recent release of surveillance videos from the Sanford police headquarters the night of the incident.
It shows Zimmerman, his hands cuffed, exiting a patrol car and being led into the police station. First broadcast Wednesday by ABCNews.com, the video does not provide close-ups, but also does not show clear signs of injuries on Zimmerman.
Zimmerman in handcuffs night of shooting 
Witness: Zimmerman 'didn't appear hurt' 
New photos show Trayvon before shooting "We now have pictures of Mr. Zimmerman walking into the police station, and you see no injuries that would have come from abrasions on a sidewalk," said Lou Palumbo, a retired police officer who owns a private security firm.
"Anyone who's seen a broken nose is aware of the fact that the blood spurts. That leads to a lot of bleeding. You would have expected to see blood on the front of George Zimmerman's shirt collar. Blood -- you know, in many more places," said Marcia Clark, the former prosecutor in the O.J. Simpson trial.
Robert Zimmerman Jr. said his brother was treated at the scene before he was taken to police headquarters and it appears to him that the surveillance tape shows that his brother had injuries.
Sybrina Fulton, Martin's mother, has said the video is among other evidence that proves her son was killed unjustly.
Opinion: Martin's death more than teachable moment
"I believe that this video is the icing on the cake," she said. "This is not the first part of the evidence that they have had. They have had the 911 tapes and they also have witnesses. This is in addition to what the Sanford Police Department has always had. There is no problem with this case and he needs to be arrested."
A witness of the incident also spoke to CNN Thursday.
"It would have to be starting with hearing voices, but not seeing, and then, after the voices, opening a window and then seeing -- with two men or two people on the ground, one on top of each other," the witness, who has asked not to be identified, even by gender, told CNN's Anderson Cooper about the incident.
The witness reported hearing through a closed window voices from an area where residents typically walk their dogs. "I thought it was rather loud, but I had just shut my window because it had just started pouring out rain," the witness said. "And then I thought, 'Oh, my gosh, who's out there walking their dog in the rain?' "
In Depth: CNN peels back the layers
But the witness did not immediately look outside to see what the commotion was about, according to the account. "I went and did something else, and then I heard the loud voices again," said the witness, who reported opening the window. "It definitely was a very loud, predominant voice," the witness said. "I couldn't hear the words but it was like, OK, this is not a regular conversation. This is someone aggressively, you know, yelling at someone."
The witness recounted seeing two men on the grass, one on top of the other. "And at that point, not looking out the window, I heard the yell for help, one yell for help, and then I heard another ... excruciating type of yell. It didn't almost sound like 'help.' It just sounded so painful. But I wasn't watching out the window during that. And then the next time I looked out the window, there's the same thing: two men on the grass, one on top of each other. I couldn't see a lot of movement. It was very dark, but I felt like they were scuffling. And then I heard the gunshots, which, to me, were more like pops than they were like a bang."
The witness recalled hearing more than one shot. "It definitely was more than one pop noise, so I don't know if it was an echo or anything else. But it definitely made more than one pop."
The witness said the shots were audible as one man was on top of the other. But the witness recalled not having been able to see clearly which man was on top because it was dark.
Within a couple of seconds after the shots, one of the men "was walking toward where I was watching, and I could see him a little bit clearer. Could see that it was a Hispanic man. He didn't appear hurt or anything else."
But the man, who by now had left the grass and was walking on the sidewalk, did seem worried, "with his hand up to his forehead," the witness said. "Now, a couple of seconds later, in the dark, you see that person that's alive walk away; you know, obviously, OK, he must've got up and he walked away, where the other person is still laying there, face down."
The person who was walking away did not appear hurt, said the witness, who has told police of the incident. "You're thinking, wow, I'm looking at the person that just shot someone," the witness said.
CNN's Umaro Djau, Deirdre Walsh, Ed Payne and Tracy Sabo contributed to this report.
