Prosecutors have released video footage of Trayvon Martin buying sweets and a drink in a Florida convenience store minutes before he was shot and killed in a confrontation with a neighbourhood watch leader.

The scenes recorded at the 7-Eleven close to the Retreat at Twin Lakes development in Sanford show Martin, 17, wearing a black hooded top and beige trousers, walking up to the counter and paying.

Soon after leaving the shop Martin got into a fight with George Zimmerman, who had already called police to report a "suspicious" black male in the neighbourhood. Martin was shot dead by a single shot to the chest at point-blank range, the gunshot heard on recordings of several 911 calls made by neighbours.

The video is among the latest in a batch of evidence released on Friday by prosecutors who have charged Zimmerman, 28, with second-degree murder.

It represents the first public glimpse of the unarmed teenager on 26 February, the night he was killed in an incident that led to race protests and the resignation of the local police chief. The Sanford police department originally released Zimmerman without charge after he claimed he acted in self-defence, and he was arrested in April only after the appointment of a special prosecutor to re-examine the evidence.

The haul of evidence released by state attorney Angela Corey's office over the last two days includes a toxicology report that showed Martin had traces of marijuana in his system, medical records confirming bloody injuries to Zimmerman's head, and testimony by Martin's father that it was not his son's voice heard on 911 recordings crying for help.

Additionally, there were numerous witness statements, many contradicting each other over such details as how many shots were fired and which of the two was on top of the other during their fight. And one police report reveals that detectives wanted to charge Zimmerman with manslaughter even after Bill Lee, then the chief of the Sanford police department, had told reporters there was insufficient evidence to justify such a charge.

The confrontation was "entirely avoidable", detective Chris Serino wrote, if Zimmerman had returned to his car or engaged Martin in conversation.Among the various audio recordings of interviews with witnesses is one of a teenage girl in Miami, where Martin lived, who told prosecutors she was on the phone to her friend and heard Zimmerman approach him.

The girl, whose identity has not been revealed, said she heard Martin say: "Why you following me for?"

She said: "I hear this man, like this old man, say, 'What are you doing around here?'" then said she heard a bumping sound followed by what she thought was a scuffle.

"I could hear it a little bit, 'Get off, get off,' then the phone just hung up," she said.

Zimmerman faces at least 25 years in jail if he is convicted. No date has yet been set for the trial and he remains free on $150,000 bail.

His lawyer, Mark O'Mara, warned on Friday it would be a mistake to draw any conclusion from the partial evidence so far released. "Looking at it piecemeal is what has caused some of the problems in the past with the case," he said in an interview with CBS News.

"It's sort of important that we all wait until all the evidence is out. Let's deal with it all once we have it, and deal with it in the courtroom." © Guardian News and Media 2012

This video from ABC News was uploaded to YouTube by paulus1st on May 17, 2012.