In the photos of Trayvon Martin released by his family, he looks younger than his 17 years. He looks like a little kid with a big smile. On the night of 26 February, Martin was walking to his father’s girlfriend’s house in the city of Sanford. He didn’t live in Salford. He lived with his mother and older brother in Miami Gardens, but he was visiting his dad for the night. They spent the evening watching a basketball game on TV, and during the halftime break, Martin walked to a nearby 7/11 to pick up some snacks. At the shop he bought a can of iced tea and a packet of Skittles. Those were the deadliest weapons he had on him: iced tea, Skittles, and a cellphone.

Martin used the cellphone to call his girlfriend. She has testified he told her he was being followed by a “strange man”, and that he was scared. She says she then heard Martin ask someone “What are you following me for?”, followed by a male voice responding “What are you doing here?” Martin’s girlfriend says that she then heard the sound of physical jostling and Martin’s cellphone went silent.

Meanwhile, there is the record of a phonecall made to the emergency number 911 shortly before this. In the recording, the caller reports Martin as engaging in “suspicious behaviour” – “just walking around looking about”. The caller said, “This guy looks like he is up to no good”. The emergency call dispatcher advised the caller not to take any action, saying that he would send a police car. The caller then informed them that Martin had “taken off”. The dispatcher asked if the caller was pursuing him. He said yes. The dispatcher told him this was unnecessary.

The caller has since been identified as George Zimmerman, 28. Zimmerman was originally reported by the media to be a Neighbourhood Watch official for the area, but now the idea that he took on this role in any kind of official capacity is disputed. It seems Zimmerman may have been a self-appointed watchman: the National Sheriffs’ Association, which runs the Neighbourhood Watch Programme, issued a statement saying it has “no information indicating the community where the incident occurred has ever even registered with the NSA Neighbourhood Watch programme”.

What is clear is that Zimmerman was preoccupied, to the point of obsession, with the safety of his neighbourhood. Between 1 January 2011, and the night of Martin’s shooting, he made almost 50 calls to 911, reporting individuals and incidents that he found suspicious within his community – ranging from the spotting of two black males he thought might fit the profile of suspects from a recent robbery, to the fact that a neighbour’s garage door was open.

As for what happened next, that depends on whose story you believe. George Zimmerman says after having called 911, he returned to his truck to await the police car they said they had dispatched, only to be jumped on and attacked from behind by Martin. Zimmerman then says he shot Martin in the chest with his semi-automatic handgun because he feared for his life. There are conflicting witness accounts. One witness endorses Zimmerman’s version of events, saying he saw Martin beating Zimmerman up. Another witness, Mary Cutcher, said she and her housemate heard no signs of a scuffle at all – only a young voice whining and crying, followed by a gunshot, and then seeing Zimmerman pinning Martin on the ground with his knees.

In some ways it is what happened next that has become the real story, however. Police tested the body of Trayvon Martin for traces of drugs and alcohol. (They found none.) They were happy, however, to simply take Zimmerman’s word for it that the older man had no drugs or alcohol in his system – no testing was carried out on Zimmerman. Trayvon’s father, Tracy Martin, has said that the family was told by police that they believed Zimmerman’s account of events in all respect because he had a “squeaky-clean record”. This turned out to be not quite true, however.

In July 2005 Zimmerman had been arrested after a tussle with security outside a bar in Florida, but because it was a first offence, he escaped with a “pre-trial diversion programme”. The same year, the Daily Beast notes, an injunction was filed against him by a woman claiming charges of domestic violence against him. The injunction was granted. In 2008 he reached a settlement with a credit card company, Capital One, after falling behind with payments.

But police seemed more interest in the criminal background of Trayvon Martin, carrying out a full check on the dead boy, which failed to bring up a speck of dirt. Martin was reportedly a good student (he received A and B grades), who hoped to study further. On a website set up by Martin’s parents, they describe him as “our hero”. They wrote: “At the age of nine, Traycon pulled his father from a burning kitchen, saving his life. He loved sports and horseback riding. At only 17 he had a bright future ahead of him with dreams of attending college and becoming an aviation mechanic. Now that’s all gone.”

Police did not arrest George Zimmerman, and neither did they charge him with any offence. This was permissible on their behalf thanks to Florida self-defence laws. Since 2005, Florida law has included a “Stand Your Ground” premise, under which an individual who perceives their life to be under threat can defend themselves without needing to try to get away. Prior to 2005, you needed to be able to prove that you had used deadly force as a last resort. Since the passing of the “Stand Your Ground” law, technically known as the ‘Castle Doctrine’, this caveat no longer exists. CBS Miami reported this week that since the law was passed, deaths in which self-defence is claimed have risen by over 200%.

As a result of the Stand Your Ground law, in fact, police could not only get away with not arresting Zimmerman, but were legally prevented from doing so. This is their defence, in any case. This week the city manager of Sanford released a letter which read: “Mr Zimmerman provided a statement claiming he acted in self defence which at the time was supported by physical evidence and testimony. By Florida Statute, law enforcement was prohibited from making an arrest based on the facts and circumstances they had at the time.”

The situation may be a little murkier still. Despite the Sanford police chief Bill Lee’s claim that he carried out a “fair and thorough investigation” three weeks ago, the police stand accused of having failed to follow up on important leads – such as the testimony given by Martin’s girlfriend about the cellphone conversation. Then there’s the claim by Mary Cutcher that after she gave evidence to police, they “corrected” her statement to make it agree with Zimmerman’s. She said it appeared to her at the scene of the shooting the police “were siding with him from the start”.

Now there’s also the claim that police missed a racial slur uttered by Zimmerman on his 911 call. Officers told ABC News this week that they may have overlooked a moment in the recording where Zimmerman may have said the phrase “fucking coons” under his breath, though some audio experts say that he more likely said “fucking punks”.

MSNBC host Lawrence O’Donnell went so far as to describe this as “evidence of a police cover-up”.

This week it was announced the shooting will be the subject of three investigations. One carried out by the Sanford police department, one by the US justice department with the FBI, and one by the Florida state attorney. However, it’s fair to say the only reason the matter is being taken further now is because of the outcry that has been growing over the past three weeks, led largely by Martin’s family, black lawyers and civil rights activists. A petition calling for Zimmerman’s arrest has now attracted more than 800,000 signatures. But as The Guardian’s Gary Younge notes, “It is not at all uncommon for young black men to leave the world in a shower of bullets followed by deafening silence.”

In some ways Zimmerman’s assumption that Martin must be up to no good was not illogical given the social context, Younge writes. Almost one in 10 black men in America are in prison, and they are more likely to be stopped and searched than any other group. “To assume that when you see a black man you see a criminal is rooted in the fact that black men have been systematically criminalised,” Younge writes. “That excuses nothing but explains a great deal”.

The investigation into Martin’s death may cause a rethink of Florida’s Stand Your Ground law, which many will welcome. Sanford police chief Bill Lee will also be lucky to hold on to his job in the face of mounting public outrage. It remains to be seen if any change will be brought about in the American justice system. DM

Read more:        

• Trayvon Martin: a killing too far in The Guardian.  

Photo: Tracy Martin, father of slain Florida teen Trayvon Martin, joins a protest called ‘A Million Hoodies March’ to demand justice for his son’s death, in New York’s Union Square on 21 March 2012. Martin, 17, wore a hooded sweatshirt when he was killed last month in a gated community in Sanford, Florida, by neighborhood watch volunteer George Zimmerman. REUTERS/Andrew Burton.