On the night of the shooting, door-to-door canvassing was not exhaustive enough, said a law enforcement official familiar with the investigation. If officers had been more thorough, they might have determined that Mr. Martin, 17, was a guest — as opposed to an intruder — at a gated community called the Retreat at Twin Lakes. That would have been an important part of the subjective analysis that night by officers sizing up Mr. Zimmerman’s story. Investigators found no witnesses who saw the fight start. Others saw parts of a struggle they could not clearly observe or hear. One witness, though, provided information to the police that corroborated Mr. Zimmerman’s account of the struggle, according to a law enforcement official.

¶ The police took only one photo at the scene of any of Mr. Zimmerman’s injuries — a full-face picture of him that showed a bloodied nose — before paramedics tended to him. It was shot on a department cellphone camera and was not downloaded for a few days, an oversight by the officer who took it.

¶ The vehicle that Mr. Zimmerman was driving when he first spotted Mr. Martin was mistakenly not secured by officers as part of the crime scene. The vehicle was an important link in the fatal encounter because it was where Mr. Zimmerman called the police to report a suspicious teenager in a hooded sweatshirt roaming through the Retreat. Mr. Zimmerman also said he was walking back to the vehicle when he was confronted by Mr. Martin, who was unarmed, before shooting him.

¶ The police were not able to cover the crime scene to shield evidence from the rain, and any blood from cuts that Mr. Zimmerman suffered when he said Mr. Martin pounded his head into a sidewalk may have been washed away.

¶ The police did not test Mr. Zimmerman for alcohol or drug use that night, and one witness said the lead investigator quickly jumped to a conclusion that it was Mr. Zimmerman, and not Mr. Martin, who cried for help during the struggle.

¶ Less than two full days after the shooting a woman called an investigator. She refused to identify herself or give any callback numbers, but told the investigator that Mr. Zimmerman “has racist ideologies and that he is fully capable of instigating a confrontation that could have escalated to the point of Zimmerman having to use deadly force.”mThe police were never able to track her down. [MORE]