City of Sanford issues letter explaining why George Zimmerman was not arrested as public outcry continues to escalate

As public anger continues to grow over the shooting death of unarmed black teenager Trayvon Martin in Florida, the city of Sanford issued a letter with answers to questions put to the police chief to explain why the known killer is still free.

The letter, signed by city manager Norton Bonaparte, reiterates the previous reasoning by Sanford police chief Bill Lee which said he could not carry out an arrest because self-appointed neighbourhood watch volunteer George Zimmerman said he acted in self-defence.

The letter states:

Mr. Zimmerman provided a statement claiming he acted in self defense 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.

It provided new information about Zimmerman's statement to police: "Zimmerman's statement was that he had lost sight of Trayvon and was returning to his truck to meet the police officer when he says he was attacked by Trayvon."

Up until now, evidence in the public domain – the 911 tape of Zimmerman – suggested he had been following and pursuing Martin.

Lee is facing calls by civil rights leaders to resign. He has insisted that he carried out a "fair and thorough" investigation of the killing and that he cannot arrest Zimmerman because he told police he shot the teenager in self-defence and there was no evidence to contradict his account.

Criticism of the police investigation is also focused on the failure to test Zimmerman for drugs or alcohol, a common practice in homicide investigations, in particular because they tested the teenager after his death.

Police are also facing questions over their failure to reach Martin's girlfriend in Miami, who was talking to him on his cellphone as he was being followed by Zimmerman in the minutes before his death. She said his last words were "What are you following me for?"

George Zimmerman and Trayvon Martin. Photograph: Orlando Sentinel

Martin's family say the girlfriend's testimony of the call undermines Zimmerman's self-defence claims. There have also been reports that police "corrected" witnesses who say they heard the boy screaming for help.

This week, police admitted to ABC News they may have missed a potential racial slur on the tape of Zimmerman's 911 call to report Martin's "suspicious behaviour".

Ben Jealous, president of the National Association for the Advancement of Colored People told Miami television channel NBC6 that federal authorities should take over Lee's department because of a "pattern and practice of discrimination" which include cases that precede Martin.

At a highly-charged town hall meeting at Allen Chapel AME Church in Sanford on Tuesday night, Jealous told the 350-strong crowd: "Any chief who would so allow his officers to so mishandle a situation like this has to go. We will ensure that there is a new chief here in Sanford."

Hundreds more gathered outside, chanting "I am Trayvon Martin."

The calls for Lee's resignation came as Florida governor Rick Scott, who attended a meeting with black lawyers and civil rights activists on Tuesday night, said it was time to revisit the state's controversial "Stand Your Ground" law. This allows people to use deadly force if they feel endangered, without requiring them to retreat from the threat.

"If there's something wrong with the law that's in place, I think it's important we address it. I'm going to look at it. If what's happening is it's being abused, that's not right. We all want to live in a safe place," Scott told the Palm Beach Post News.

In New York, a "one million hoodie" march is planned for Wednesday evening, with Martin's parents Sybrina Fulton and Tracy Martin due to attend, according to NBC New York.

"A black person in a hoodie isn't automatically 'suspicious'," says the event's Facebook page, which calls on people to "show the world we are all Trayvon" by uploading a photograph of themselves on social media sites wearing hoodies with the hashtag #millionhoodies.

Almost 800,000 people have signed a petition on the Change.org website calling for Zimmerman to be prosecuted.

Set up by Martin's parents, it describes him as "our hero". They said: "At the age of nine, Trayvon 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."

Local pastors and members of the Florida Civil Rights Association planned a rally outside the Florida Division of Licensing in Orlando to demand that Zimmerman's concealed weapons permit be revoked, according to the Orlando Sentinel.

The group leader J Willie David earlier claimed the 28-year-old man is a "clear threat to public safety".

The case is now the subject of three investigations, including the Sanford police department. The US justice department, along with the FBI, launched an inquiry this week, after the case garnered national attention. On Tuesday the Florida state attorney for Seminole and Brevard counties announced that a grand jury would hear evidence.