George Zimmerman shot and killed Trayvon Martin on February 26
New details released Thursday show how police crafted their case
Martin was pronounced dead minutes after police arrived
Zimmerman had a bloody nose and head, photographs show
(CNN) -- Trayvon Martin walked into a 7-Eleven in Sanford, Florida, grabbing a bag of Skittles and a can of Arizona iced tea. The hood from his dark gray sweatshirt over his head, he walked up to the counter, reached deep into his pants' pockets, paid the clerk, then walked out.
This seemingly mundane act, captured on a surveillance video, would be the last image the 17-year-old's loved ones would have of him alive.
While questions still remain, what happened next to Martin on the night of February 26 became clearer on Thursday with the release of scores of pages of investigative and medical examiner's reports, in addition to new images of Martin's shooter and the 7-Eleven video.
Martin didn't live in Sanford, a central Florida city of about 53,000 people. Yet by that winter night, he'd been there for seven days, after being suspended for the third time from Dr. Michael M. Krop High School in Miami, in this instance, for 10 days after drug residue was found in his backpack, according to records obtained by the Miami Herald.
His father Tracy had taken his son four hours away from home because neither he or Trayvon Martin's mother wanted the teen to stay in his hometown where he could enjoy time with his friends, family friend and former football coach Jerome Horton recalled later.
That Sunday night, Martin was supposed to be getting a snack and heading back to the Sanford home of his father's fiance.
It was on that walk back that he encountered George Zimmerman, a 28-year-old neighborhood watch volunteer.
Some details as to Martin's thought process around that time may someday be gleaned from what he told his girlfriend back in Miami in a cell phone conversation, his family's lawyers said.
The boyfriend and girlfriend spoke at 7:12 p.m.
Zimmerman's voice, meanwhile, comes through on a 911 call he made around that time, telling a dispatcher about "a real suspicious guy."
"This guy looks like he's up to no good, or he's on drugs or something. It's raining, and he's just walking around."
The dispatcher asked Zimmerman, who'd called 911 at least four times previously for other incidents, if he was following the person. He replies, "Yes."
"OK. We don't need you to do that," the dispatcher responded.
But Zimmerman followed him anyway.
What happened next is a matter of dispute. Martin and Zimmerman were obviously in the middle of it, but no one else saw all that happened. One witness later told police that "she heard a commotion, which sounded like arguing," while another mentioned "loud talking."
And on one 911 call, placed by a neighbor, a police sergeant counted one man yelling "help!" or "help me!" 14 times in a span of 38 seconds.
Who was yelling? When the 911 calls were later played back for him and he was asked if they were from his son, an emotional Tracy Martin "quietly responded 'no'." But an FBI analysis, also detailed on Thursday, said it couldn't be determined whose voice it was due to the "extreme emotional state" of whomever was yelling, a lack of words from which to compare, overlapping voices and "insufficient voice quality" on the recording.
The same analysis also didn't reach conclusions as to whether Zimmerman used a racial epithet to describe Martin on his own 911 call, as some have alleged. Martin's family have said they believe Zimmerman, a white Hispanic, profiled the African-American teen.
Numerous witnesses, however, did clearly hear a gunshot.
It came from Zimmerman's black, 9mm semiautomatic hand gun. The bullet went into Martin's left chest and lodged there.
Police headed to the neighborhood after Zimmerman's initial 911 call, but didn't arrive until after the fatal shot. They found Martin "face down in the grass."
A sergeant checked and couldn't find a pulse. For the next six minutes, he and another police officer teamed up to conduct CPR on the teen. A plastic bag, brought by a neighbor, was used to seal his chest wound. Firefighters and EMS from the Sanford Fire Department arrived at 7:27 p.m., to continue efforts to try to save him.
Aside from a small scratch on one finger, that gunshot wound was the only apparent injury the teenager suffered. A medical examiner's report later found trace elements of THC, an element of marijuana, in his system, though experts pointed out the challenge in equating the levels found with Martin's level of intoxication at the time of his death.
One officer who lifted Martin's shirt at the scene "felt a large, cold can in the center pocket" of the teen's hoodie, which was the iced tea he'd bought just minutes before. Blood was later spotted on his Skittles, along with a lighter, a T-Mobile brand cell phone, headphones and $40 and some change.
A witness told police that, after the gunshot, she saw a "larger" man standing over Martin.
Police who arrived described the shooter, Zimmerman, as compliant in answering their questions and willingly putting on handcuffs.
He had blood on his nose -- with one officer saying it appeared "broken," while noting "swelling" of his face -- and, as photographs showed, blood on the back of his head. His back was wet and soiled, as if he'd been in grass.
Zimmerman claimed that Martin had attacked him, hitting him in the nose and knocking him back into the pavement. It was only then, in self-defense, that he'd taken out his gun and shot the teen, he said.
Tests, the results of which were made public Thursday, would show evidence of Zimmerman's hands on the firearm, but not Martin's. An analysis of scrapings from underneath the teenager's fingernails did not contain any of Zimmerman's DNA, as might rub off in the case of a prolonged struggle.
At the scene, Zimmerman declined to be transported to the hospital despite his apparent injuries.
A police officer reiterated that offer after Zimmerman complained his head hurt and he felt lightheaded while being driven to the Sanford Police Department. But again he turned it down.
While at the police station, Zimmerman requested some tissues, water and to go to the bathroom, but little else. He ended up turning over his clothes to police but, after being questioned and putting on a change of clothes brought in by his wife, he headed home.
Tracy Martin, meanwhile, didn't know where his son was. He filed a missing person's complaint on the morning of February 27, telling authorities that his son hadn't returned from going to the store the previous evening.
Police had declined to arrest him that night, saying there wasn't enough evidence to refute his self-defense claim.
But the investigation continued. In a capias request, a request that someone be taken into custody, on March 13, police described what happened as "ultimately avoidable by Zimmerman, if Zimmerman had remained in his vehicle and awaited the arrival of law enforcement, or conversely if he had identified himself to Martin as a concerned citizen and initiated dialog (sic) in an effort to dispel each party's concern.
"There is no indication that Trayvon Martin was involved in any criminal activity."
On April 11, special prosecutor Angela Corey announced that Zimmerman was being charged with second-degree murder.
He was subsequently arrested and, eventually, released on bail. The start of his scheduled trial has not yet been set.