George Zimmerman, 28, has said he shot Travon Martin the night of Feb. 26 in a gated community in Sanford, Fla., after the unarmed 17-year-old punched him in the nose and knocked him down so his head hit the ground.
The first police report on the incident indicated Zimmerman was bleeding from his nose and the back of his head, and Zimmerman's lawyer has said the neighborhood watch volunteer's nose was broken in the alleged altercation.
The police video, which ABC said Wednesday it had obtained exclusively, shows Zimmerman getting out of a Sanford police cruiser with his hands cuffed behind his back and being frisked, but there is no readily evident sign of blood or injury. The video shows a police officer looking at the back of Zimmerman's head.
A 16-year-old friend of Martin's -- who was on the phone with him when he was killed and says he told her during the call he was being followed as he was returning from a convenience store where he had gone for a soft drink and candy -- told ABC News police had not interviewed her.
"When he saw the man behind him again he said this man is going to do something to him," said the girl, who is being identified only as DeeDee. "And then he said this man is still behind him and I said run."
She said she heard Martin, who was black, ask Zimmerman, who is white, why he was following him and then heard the man ask Martin what he was "doing around here."
The police department requested an arrest warrant from the Seminole County State Attorney's office early on, but was overruled by the prosecutors, special prosecutor Angela Corey told The Miami Herald.
"I can tell you that the police went to the state attorney with a capias request, meaning, 'We're through with our investigation and here it is for you,'" Corey told the newspaper.
A capias is a request for charges to be filed.
A Sanford police report indicated the case was categorized as "homicide/negligent manslaughter," the Herald said.
"The state attorney impaneled a grand jury, but before anything else could be done, the governor stepped in and asked us to pick it up in midstream," she said.
Gov. Rick Scott replaced Seminole State Attorney Norm Wolfinger with Corey, a state attorney in Jacksonville, Fla.
The Seminole County state attorney's office declined to comment on whether its prosecutors ever recommended against filing charges.
ABC News reported Chris Serino, the lead homicide detective on the case, recommended charging Zimmerman with manslaughter the night of the shooting.
The network said Serino was instructed not to charge Zimmerman after Wolfinger's office said there was not enough evidence to prosecute the case.
Zimmerman, an insurance underwriter and college student, was not charged, triggering a nationwide crusade on the dead teen's behalf.
Earlier statements by Bill Lee, the Sanford police chief who has since stepped aside temporarily, indicated there was no probable cause to arrest Zimmerman.
Several prosecutors have said it would be difficult to try Zimmerman because of the state's so-called stand-your-ground law, allowing people in Florida to shoot others if they feel threatened with serious harm or death.