In the twisting and turning controversy surrounding the Trayvon Martin shooting, even evidence that appeared to support one side last week can tell a different story this week.
A newly enhanced version of surveillance video from the night the teenager was shot in Sanford more clearly shows a possible gash or injury on the back of shooter George Zimmerman's head.
ABC News on Monday debuted the new video in which an apparent wound of some kind can be seen on Zimmerman's head when he turns away from the camera.
The video is an enhanced version of surveillance tape released by the Sanford Police Department last week. It shows Zimmerman being taken into SPD headquarters after the shooting.
Though legal experts downplayed its importance at the time of its release, the video was taken as evidence that Zimmerman had exaggerated or falsified his self-defense claim.
Zimmerman told investigators in the case that the South Florida teen attacked him, punched him to the ground and slammed his head into the pavement in the moments before he fired the fatal shot.
At ABC News' request, the video was enhanced by Forensic Protection Inc., a California video- and audio-enhancement firm.
FPI President Douglas Carner said the video released by police had very little so-called "noise" — a term for the grainy, excess pixels that sometimes appear in such video, particularly at night.
Carner told the Sentinel in an interview Monday that the largest issue with the video was the focus. The cameras were focused on set points inside and outside of the Police Department and not on Zimmerman's head.
Here's how FPI says it conducted the enhancement:
Carner said they used the badges on officers' uniforms to refocus the video. Once a setting was found at which the badges appeared clearly, they applied it to Zimmerman's head.
Carner compared it to work he has done in bar-fight video. In bars, he said, the camera is usually focused on the register.
"They'll be video of a fight in front of a bar," Carner says. By digitally refocusing, he says, "the cash register goes out of focus and the fight scene slides into clearer view."
Zimmerman was seen by paramedics after the shooting, a police report indicates. An initial police report noted that he was bleeding from the nose and the back of the head. He was interviewed and released without being arrested. A special prosecutor is reviewing the case.
Slur or no slur?
In a Sentinel report Sunday, two forensic audio experts analyzed a 911 call made on the night of the shooting and said it was not Zimmerman crying for help in the moments before the fatal gunshot was fired.
The report challenged a key element in Zimmerman's self-defense claim and sparked an increased focus on the audio evidence in this case.
A call Zimmerman made that night, in which he reported Trayvon as suspicious, has fueled the controversy in several ways.
"This guy looks like he's up to no good, or he's on drugs or something," Zimmerman told a police dispatcher as he watched Trayvon minutes before the shooting.
Based on that description — and the fact that he was quickly suspicious of the teen — many have accused Zimmerman of racial profiling, or worse.
But some insist that he went a step further, uttering an expletive and a racial slur under his breath during the call.
The portion of the call with the potential slur lasts less than a second but may have an impact on the controversy. The Federal Bureau of Investigation and the U.S. Department of Justice are looking into possible civil-rights violations.
So what does Zimmerman say?
"I believe I know what I'm hearing, and I believe it is [the racial slur]," says Ed Primeau, a Michigan-based voice-forensics expert who provided the Sentinel an enhanced version of the audio.
The Sentinel is not publishing the slur that some say they hear on the recording. However, the excerpt that Primeau provided can be heard online at OrlandoSentinel.com.
"I used some equalization to remove some of the wind noise," Primeau says, producing a clearer sample of the audio. Then he compressed the audio and re-listened to it, taking the events that lead to the moment into account.
However, Maine-based audio engineer and forensic-audio enhancement expert Arlo West also analyzed the audio, and he came to a different conclusion.
West declined to reveal last week what he thinks Zimmerman says. However, he said he hears Zimmerman say three words, including an expletive but no racial slur — not two words, as those who hear the slur claim.
Both West and Primeau are working members of the American College of Forensic Examiners International in the field of recorded evidence.
In an interview last week, West said a number of issues can come into play when he's tasked to coax words from a recording like the Zimmerman tape.
Environmental factors, such as background noise and other sounds with similar frequencies to human speech can make separating a voice from a recording difficult, he said.
In the 911 call, Zimmerman is breathing heavily, and he says the phrase in question very quietly.
"Let's face it, whispering is whispering," West says. In teasing out difficult-to-isolate speech, "you have to be very careful as an expert that you don't make it worse."
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