George Zimmerman, the killer of black Florida teenager Trayvon Martin, was a neighbourhood busybody who once called police to complain about children playing in the street, but there was nothing to suggest that he was a racist, according to the FBI.

Federal agents interviewed many of the neighbourhood watch leader's friends, colleagues and family members as part of their civil rights investigation into the 26 February shooting but found nobody who believed Zimmerman, 28, was motivated by racial bias.

Instead, they found that most of the interviewees had a generally favourable opinion of him, with even the lead detective in the case convinced that he pursued Martin through a Sanford gated community because his suspicions were aroused by the teenager's clothes, not because he was black.

The new details come in a second wave of evidence in Zimmerman's second-degree murder case released publicly on Thursday by special prosecutor Angela Corey.

As well as the FBI records, the documents contain police reports that reveal detectives had differing opinions about the extent of the injuries Zimmerman claimed to have received in the altercation with Martin, 17.

And they show that Zimmerman, who denies murder on the grounds of self-defence, was keen to become a police officer himself and was a regular at local gun ranges and ammunition shops.

His former fiancée Veronica Zuazo, who in 2005 sought a restraining order against him citing domestic violence, told investigators: "He often talked about wanting to be a police officer."

In his role as neighbourhood watch captain for the Retreat at Twin Lakes community, Zimmerman, who was released on $1m bail last Friday to await his trial for second-degree murder, made several calls to police in the months leading up to the shooting.

In one, transcripts show, he reported that children were playing and running into the street. "It's habitual," he complained. "I'm just concerned for their safety and drivers in the neighbourhood."

Four other calls concerned black men he had spotted in the community that he considered "suspicious". He said the same thing to emergency dispatchers about Martin in a call immediately before he became engaged in the confrontation with the younger man who was walking to the house of his father's friend carrying sweets and a drink he had just bought.

Martin, who was visiting from Miami, was wearing a hooded top when he was shot. Detective Chris Serino of the Sanford police department told the FBI he believed Zimmerman followed him "based on attire" and not the colour of his skin.

Zimmerman, Serino said, possessed a "little hero complex" and was "overzealous" but he was not a racist.

Meanwhile, it appeared that Zimmerman's previously poor opinion of the Sanford PD was reversed when he spent an evening as a civilian observer on patrol with a female officer and liked what he saw.

"In the past, I have not had a positive perspective," he wrote in an email to Bill Lee, the chief of the police department who was sacked last month after a furore over the original decision not to charge Zimmerman. "Faith restored," he added.

All of those interviewed were asked if they thought the defendant displayed "any bias, prejudice or irrational attitude against any class of citizen, religious, racial, gender or ethnic groups".

In a unanimous response likely to please Zimmerman's lawyer Mark O'Mara, none did. O'Mara has insisted his client is no racist and that it was Martin who was the aggressor, punching and breaking Zimmerman's nose.

Detectives debated the severity of Zimmerman's injuries after the incident, the newly released records show, with some believing his nose to be broken and others disputing it. The extent of the injuries could be crucial to O'Mara's case as he tries to get charges dismissed under Florida's controversial stand-your-ground law, which allows for the use of deadly force if a person feels their life is in danger.

Also in Thursday's release were several photographs of evidence in the case, including one of Martin's hooded sweatshirt featuring a small bullet hole in the torso area surrounded by a bloodstain. He was killed by a single shot.

Zimmerman faces up to life in prison if he is convicted at a trial not expected to take place before next year. His wife, Shellie Zimmerman, 25, is charged with perjury for lying about the couple's finances at a bail hearing in April.